Name: Sourdough Lemon Bars
Prep time: 20 min
Cook time: 1 h
Total time: 4 h 20 min
Yield: 16
Cuisine: American
Ingredients: 158 g (12 tablespoons) butter; 75 g (1/3 cup) granulated sugar; 60 g (approx. 1/4 cup) sourdough starter, active or inactive; 1 tsp lemon zest (approx. 1 lemon); 2 tsp vanilla extract; 1/2 tsp salt; 220 g (1 1/2 cup) all-purpose flour; 3 large, whole eggs (150 g); 200 g (1 cup) granulated sugar; 60 g (approx. 1/4 cup) sourdough discard, active; 1 lemon, zested; 2 lemons, juiced (110 g or 1/2 cup); 80 g (1/3 cup) whole milk; Powdered sugar for dusting (optional)

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Sourdough lemon bars are bright, creamy, and delicious. The decadent lemon filling is made with sweetened fresh lemons and tangy sourdough discard. And it sits on a thick, buttery sourdough shortbread crust. These cheerful treats are perfect for sunny picnics and summer gatherings.

Woman's hand hold sourdough lemon bar with lemon bars and flowers in the background

Table of Contents

When it comes to summer food, give me ALL of the fruit, please! We devour sourdough peach cobbler for as long we can get our hands on South Carolina peaches. I toss local blueberries in a homemade blueberry-bourbon BBQ sauce.

And, of course, as a self-proclaimed lemon lover, I welcome anything lemony. From creamy lemon chicken to sourdough lemon bars, I can’t get enough lemon this time of year.

That’s especially true lately because it has been unseasonably hot here in southeastern North Carolina. Luckily, these sourdough lemon bars are like a cold glass of lemonade on a hot day.

The fresh lemon juice, lemon zest, and sourdough starter are perfectly balanced with a little sweetness and a buttery shortbread crust. And they are served cold, which is divine after a long, hot day in the sun.

Sourdough lemon bars are a classic dessert with added sourdough starter for an elevated and unique twist. You won’t be able to get enough of them!

About This Recipe

The filling is an adaptation of Brown-Eyed Baker’s Lemon Bars adjusted to include sourdough starter.
The crust is an adaptation of Inspired Taste’s shortbread crust, but with a tangy sourdough twist. I also make them in an 8″x8″ baking dish to create a thicker crust.

Video – Sourdough Lemon Bars

Why You’ll Love This Recipe

Use extra starter – If you have extra starter, this is a great recipe for using it up. Just be sure you use it while it’s still active and bubbly. If you don’t know the difference between the various starter stages, check out my sourdough starter overview on YouTube.
Simple ingredients – This recipe uses only nine ingredients, most of which you probably have on hand.
Lightly sweetened – I often find store-bought lemon desserts are too sweet. These sourdough lemon bars will satisfy your sweet tooth, but they have less sugar than most.
Summer treat – Summer baking, in my opinion, is completely overlooked and underrated. The flavors and textures of summer sweet treats are a dream.

Overhead of lemon bars and woman's hand holding a single lemon bar with text "Sourdough Lemon Bars"

Tips for Using Sourdough Starter in This Recipe

This sourdough lemon bar recipe calls for active starter, particularly in the lemon custard filling. Rather than cornstarch, the active starter’s flour thickens the filling.

Here are a few simple tips for using sourdough starter in this recipe:

Use active starter

An active sourdough starter contains more flour, which can help thicken the lemon curd. However, it also has less sour flavor, so it won’t outshine the lemon.

To ensure your starter is active, feed it within 12 hours of making lemon bars. How far in advance you feed your starter depends on its overall strength and health, as well as the environmental conditions.

Make sure your starter is doubled and bubbly when using it for the lemon filling. I recommend letting it ripen at room temperature so it is easier to combine into the egg mixture.

SOURDOUGH SUCCESS TIPS: If you want to speed up how fast your starter activates, use a proofing box. Also, if you have an inactive starter stashed in the fridge, learn how to reactivate your starter before using it.

Close up of active sourdough starter in glass jar

Use 100% hydration sourdough starter

Most home bakers use 100% hydration starter, meaning it is fed with equal parts flour and water.

There are various reasons why you might adjust the hydration. However, 100% hydration sourdough discard is best for lemon bars because it ensures the proper liquid ratio in the filling.

Sourdough lemon bars sliced and laid out on marble tabletop

Tools You Will Need

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Stand mixer or hand mixer – I like to use my KitchenAid stand mixer, but a hand mixer will also work. You can also mix the ingredients by hand.
Bowls – If you aren’t using a stand mixer, grab a large bowl to mix the dough. You will also need a small bowl for the lemon filling mixture.
Whisk or Danish dough whisk – I use my regular whisk to mix most of the ingredients, but I switch to a D anish dough whisk to combine the sourdough starter into the lemon filling.
Measuring cups and spoons – This is a forgiving recipe, so grab your measuring cups and spoons if you don’t have a kitchen scale. All of the ingredients have cup measurements listed.
Kitchen scale – If you like to bake with a little more precision, I’ve included the weight of the recipe ingredients.
Zester – A box grater will work for zesting, but the most efficient tool is a handheld zester.
Juicer – I use a lemon juicer to help keep out the pulp and seeds.
Baking dish – You will need an 8×8 baking dish. I use a ceramic dish, but a glass pan will work well, too. Though I haven’t experienced it, some bakers claim baking in a metal pan can give your lemon bars a metallic taste.
Parchment paper – Lining the baking dish with parchment paper makes it easy to clean up quickly.

Ingredients

Sourdough Shortbread Crust

Butter – I use unsalted butter. When I remember, I leave it on the counter to soften, but you can also soften it in the microwave or on the stove in a small saucepan. Just don’t let it get too hot.
Granulated sugar – Many lemon bar recipes call for powdered sugar, but regular old white sugar works best for this recipe.
Sourdough starter, active or inactive – Make sure your starter is fresh and recently fed.
Lemon zest – A little lemon zest in the crust adds a bright flavor to the crust.
Vanilla extract – I use homemade vanilla extract. Store-bought is a great option, too.
Salt – Salt brings out the other flavors. I usually use coarse kosher salt.
Flour – I recommend sticking with all-purpose to keep the crust light and tender.

Sourdough Lemon Filling

Whole eggs – Use large eggs. If you are using farm-fresh eggs, they can vary in size, so adjust as needed. If you are confident in accurately rehydrating freeze-dried eggs, they will work, too.
Granulated sugar – The sugar cuts the lemons’ tartness.
Sourdough discard, active – This sourdough lemon bar recipe uses only sourdough starter as the filling’s thickener.
Lemon zest and juice – I usually use whatever lemons I can find at the store: Meyer lemons or regular lemons.
Whole Milk – Milk makes these sourdough lemon bars creamy and decadent.
Powdered sugar for dusting (optional) – The light coating of powdered sugar adds a touch of sweetness and a classic aesthetic appeal.

Lemon bar squares on white plate next to pink cut flowers

How to Make Sourdough Lemon Bars

Make the Shortbread Crust

Preheat the oven to 350° F. Line an 8″x8″ baking dish with parchment paper. If your oven preheats quickly, you can wait until Step 6 to preheat the oven.

Add the butter and sugar to the bowl of a stand mixer (alternatively, you can use a hand mixer or even the good old-fashioned tools of yesteryear…a bowl and a whisk). Mix with a paddle attachment on medium speed until light and fluffy, about 2 minutes.

Add the sourdough starter, lemon zest, vanilla, and salt. Mix for another minute or so until fully combined with the butter mixture.

With the mixer on low, add the flour. Mix until just combined. Then, use your hands to form the dough into a loose ball.

Dough in glass bowl with flowers and lemons in background

Transfer the dough ball to the parchment-lined baking dish, and use your fingers to shape it into an even layer.

Use a fork to pierce the crust a few times. This will prevent it from puffing up while baking. So don’t skip this step!

Shortbread dough in baking dish shown with holes to prevent puffing up while baking

Pop the baking dish into the freezer for about 5 minutes to chill. This will help create a really lovely texture (if you are in a pinch, you can skip this step).

Bake for 25-30 minutes or until the edges are lightly browned.

Make the Lemon Filling

Meanwhile, whisk the eggs in a small bowl until the yolks and whites are combined. Add the sugar and mix thoroughly.

Pour in the sourdough discard and whisk until completely combined. Make sure there are no clumps of discard. I find using a Danish dough whisk when incorporating the starter is easiest.

Add the lemon zest, lemon juice, and milk. Mix thoroughly. Set aside.

Sourdough lemon bar filling in glass bowl with lemon zest scattered and a lemon zester

Make the Lemon Bars

When the crust is lightly browned on the edges, remove it from the oven and drop the temp to 325° F.

Give the lemon filling a stir, then pour it over the warm, lightly baked shortbread crust.

Bake 30-35 minutes or until the filling has set, the edges are lightly golden brown, and the center doesn’t jiggle.

Place the whole baking dish on a wire rack and allow the lemon bars to cool to room temperature, usually about an hour. Then, cover in plastic wrap and refrigerate for at least two hours before serving (I recommend keeping them in the fridge until they are thoroughly chilled).

Dust with powdered sugar just before serving.

Note: Bake times may vary depending on your oven. Keep an eye on your lemon bars. If they need more time, check them every five minutes until finished.

Sourdough lemon bars next to checkered yellow towel and fresh lemons

How To Store Leftover Sourdough Lemon Bars

Leftovers can be stored in an airtight container in the fridge for 3-5 days or frozen for up to 3 months.

Frequently Asked Questions

What are the white bubbles on the top of my lemon bars?

If, during the baking process, little white bubbles appear on your lemon bars, don’t worry. That’s just air floating to the surface. In my experience, sometimes, it happens more than others. It’s nothing a little powdered sugar can’t hide!

How do I know when my sourdough lemon bars are done?

They are ready to come out of the oven when the edges are light brown and the filling no longer jiggles in the center.

Can I use inactive sourdough starter?

It’s okay to use an inactive starter for the shortbread base. But you will need to use an active starter for the filling.

How do you cut sourdough lemon bars?

To cut lemon bars, warm a sharp knife under hot water. Dry it off, and make one or two cuts while it’s still warm. Repeat this process until the bars are completely cut.

Can I use bottled lemon juice?

Technically, yes. But I’ll bet my bottom dollar that you’ll like the lemon bars much better if they are made with real lemons. Real lemon has a vibrant flavor that can’t be replicated with bottled lemon juice. However, if you need lemon bars stat and all you have is the bottled stuff, it will get the job done!