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A single sourdough lemon bar on a plate, heavily dusted with powdered sugar, showcasing the luscious yellow layer of lemon filling atop a crumbly crust. A single sourdough lemon bar on a plate, heavily dusted with powdered sugar, showcasing the luscious yellow layer of lemon filling atop a crumbly crust.
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Sourdough Lemon Bars

Sweet and tart lemon bars with a sourdough discard shortbread crust.
Prep Time20 minutes
Cook Time45 minutes
Total Time1 hour 25 minutes
Course: Dessert
Cuisine: American
Keyword: Lemons, Sourdough Discard, sourdough discard lemon bars, Spring
Servings: 24 bars
Calories: 138kcal
Author: Katie

Ingredients

For the Crust

  • 1 cup all-purpose flour
  • ⅓ cup sugar
  • ½ cup unsalted butter cold and cubed
  • ½ cup sourdough discard

Lemon Filling

  • ½ teaspoon salt
  • 1½ cups sugar
  • 2 tablespoons cornstarch
  • ½ teaspoon salt
  • ¼ cup water
  • 5 egg yolks
  • 2 eggs
  • ⅔ cups lemon juice freshly squeezed for best flavor
  • 1 lemon zest

Asssembly

  • Powdered sugar

Instructions

  • Preheat your oven to 350°F (175°C). Line a 9x9 or 8x8 inch baking pan with parchment paper, or spry with cooking spray.
  • Mix flour, sugar, and a teaspoon of salt in a medium bowl. Cut in the butter with a fork, pantry cutter, or your fingers. Continue cutting in the butter until the mixture resembles coarse crumbs. Gently mix the sourdough and discard until it begins to come together. It will look like a pie dough.
    A mixing bowl with sourdough lemon bar crust mixture, where the ingredients are combined but still crumbly, ready for pressing into the pan.
  • Press evenly into the bottom of the prepared pan. Bake for 15-20 minutes until lightly golden. Remove and cool slightly.
  • Prepare the Lemon Mixture. In a medium saucepan, whisk together sugar, cornstarch, and 1/4 teaspoon of salt. Stir in the water, lemon juice, and lemon zest. Cook over medium-high heat, stirring frequently, until the mixture boils. Once the mixture reaches a boil, reduce the heat to low and let it simmer for 1 minute. The mixture should thicken considerably.
    Two side-by-side images of a lemon bar pan, the left one without the filling and the right one filled with smooth, bright yellow lemon custard.
  • In a small bowl, whisk egg yolks and eggs. Gradually whisk in about 1/2 cup of the hot sugar mixture to temper the egg yolks. This step prevents the eggs from cooking.
  • Pour the tempered egg yolks back into the saucepan. Bring the mixture to a gentle boil and continue cooking, stirring constantly, for 2 minutes. The filling should be thick and smooth.
  • Remove from heat. Add 2 tablespoons of butter and stir until fully incorporated.
  • Assemble. Pour the filling over the crust, spreading out to smooth if necessary.
  • Bake: Bake for 20-25 minutes or until the filling is set. Cool to room temperature, then chill for at least 2 hours.
    A pair of images showing the lemon filling's transformation during cooking, with the left image displaying the initial mixture and the right image showing the thickened, vibrant yellow filling after heat has been applied.
  • Finish. Dust with powdered sugar, cut into bars, and serve chilled.
    Overhead view of a baking pan with lemon bars, as powdered sugar is being sifted over them, adding a snowy layer of sweetness. Overhead view of a baking pan with lemon bars, as powdered sugar is being sifted over them, adding a snowy layer of sweetness.

Notes

Make sure your ingredients are at room temperature before you start mixing. This will make things a lot easier and smoother.
If you want a stronger lemon flavor in your recipe, you can always adjust the amount of lemon zest you add.
It's also always a good idea to chill these thoroughly before cutting for cleaner cuts.

Nutrition

Calories: 138kcal | Carbohydrates: 21g | Protein: 2g | Fat: 5g | Saturated Fat: 3g | Polyunsaturated Fat: 0.4g | Monounsaturated Fat: 2g | Trans Fat: 0.2g | Cholesterol: 64mg | Sodium: 105mg | Potassium: 24mg | Fiber: 0.2g | Sugar: 15g | Vitamin A: 193IU | Vitamin C: 3mg | Calcium: 10mg | Iron: 0.4mg