Sourdough Lemon Bars

Bright, buttery, and unapologetically lemony, these Sourdough Lemon Bars are what happens when a classic dessert meets a clever sourdough twist. With a buttery sourdough shortbread crust and a luscious lemon filling, this recipe turns sourdough discard lemon bars into a bake that feels both nostalgic and quietly clever - the kind of thing lemon lovers come back to again and again. If you're a self-proclaimed lemon lover like me, this one hits that perfect balance between sharp, sweet, and indulgent - without being cloying or heavy.

Jump to:

• Why Add Sourdough Discard To Lemon Bars?
• Ingredient Notes
• Step-By-Step Method
• Simple Tips For Best Results
• Common Problems (And How To Fix Them)
• Irresistible Variations To Try Next Time
• Storage
• More Sourdough Discard Recipes
• Sourdough Lemon Bars

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Why Add Sourdough Discard To Lemon Bars?

Sourdough discard slips into lemon bars far more naturally than you might expect - and in this recipe, it's doing real work in both layers.

In the shortbread base, sourdough starter discard adds moisture and tenderness, helping create a buttery sourdough shortbread crust that's rich but not crumbly or dry. Because discard is already hydrated, it integrates seamlessly with butter and flour, without making the base greasy or dense.

In the lemon custard filling, that gentle tang from the discard enhances the citrus rather than competing with it. Lemon and acidity are old friends, and sourdough simply deepens that flavour profile - think sharper lemon, cleaner finish, and less flat sweetness.

There's also a practical bonus: acidity acts as a mild preservative. These sourdough discard lemon bars keep beautifully in an airtight container for longer than classic lemon bars, staying fresh and sliceable for days at room temperature or in the fridge.

Ingredient Notes

You will need a 20 × 20 cm (8 × 8 in) baking tray with high rims (we used a USA metal pan, but you may also use a glass pan) and these simple ingredients:

• Unsalted butter - Gives full control over salt and creates that classic buttery shortbread crust. Let it soften slightly so it blends easily.
• Powdered sugar (icing sugar) - Keeps the shortbread tender and delicate; granulated sugar would make it too coarse.
• Sourdough starter discard - Use discard at room temperature, ideally not overly acidic or separated. Active sourdough starter works too.
• Vanilla bean paste - Optional, but rounds out the sharp lemon flavour nicely.
• Salt - Essential for balance in the shortbread base.
• Plain flour (all-purpose flour) - Provides structure without toughness.
• Granulated sugar - For the lemon custard filling; rubbing it with zest boosts aroma.
• Fresh lemons: both zest & fresh lemon juice - Real lemons are non-negotiable here. Bottled lemon juice won't give the same bright flavour. You may also use limes, just follow our Sourdough Lime Bars recipe.
• Eggs - Create structure and that luscious lemon custard filling.

Step-By-Step Method

1. Preheat the oven and line a baking dish with parchment paper, leaving overhang for easy lifting.

2. In a food processor, combine butter, powdered sugar, sourdough discard, vanilla, salt, and flour. Pulse just until a dough forms.

3. Press the shortbread base evenly into the prepared pan and prick all over with a fork.

4. Bake until lightly golden brown at the edges, then remove from the oven.

5. In a large bowl, rub lemon zest into the granulated sugar using your fingertips. 

6. Whisk in eggs, sourdough discard, and fresh lemon juice until smooth - avoid beating in air.

7. Pour the lemon egg mixture over the hot shortbread base. You're likely to see little white bubbles on top of the mixture - that's normal. 

8. Return to the oven and bake until just set in the centre.

9. Cool at room temperature, then chill thoroughly before slicing.

10. Dust with powdered sugar just before serving. Perfect lemon bars, if you ask me!

Simple Tips For Best Results

• Use a microplane for lemon zest - It extracts fragrant oils without bitterness.
• Rub zest into sugar first - This releases citrus oils and delivers the best lemon flavour.

• Don't over-whisk the filling - Too much air leads to bubbles, cracks, and a rubbery texture.
• Watch the bake times closely - Overbaking causes grainy lemon custard.
• Chill fully before slicing - The bars need time to set for clean cuts.
• Dust icing sugar just before serving - Otherwise, it dissolves into the filling.
• Use a thin, sharp knife - Heat and clean it between slices for neat edges.

Common Problems (And How To Fix Them)

Soggy base. Usually caused by a base that wasn't baked long enough. Make sure it's set and lightly golden before adding the filling. Replace 20g of flour with rice flour for a more crumbly texture, or use 20g of cornflour for a softer, melt-in-the-mouth shortbread. 

Lemon bars not setting / runny centre. Underbaked or sliced too early. The centre should be just set. Chill thoroughly before cutting.

Grainy or rubbery filling. This happens when eggs are overcooked or over-whisked. Mix gently and bake just until set. The corner bars may be a little overbaked and grainy - that's just the nature of it!

Overly sour flavour. I like tangy, cheerful treats, so these are quite lemony, but if you find them unpleasant, your sourdough starter discard may be too acidic. Avoid discard with a strong smell or visible separation of hooch.

Irresistible Variations To Try Next Time

Looking for a unique twist for your sweet treat?

• Poppy seed shortbread - Add 1-2 teaspoons of poppy seeds to the shortbread base.
• Lemon & thyme bars - Infuse the lemon curd filling with finely chopped fresh thyme for a subtle herbal note.
• Raspberry swirl lemon bars - Dot the filling with raspberry purée and gently swirl before baking.
• Coconut lemon bars - Replace a small portion of flour with desiccated coconut for texture.

Storage

Store sourdough lemon bars in an airtight container at room temperature for up to 2 days, or refrigerate for up to 5 days.

For longer storage, freeze individual slices wrapped in plastic wrap and placed in a freezer-safe container. Defrost overnight in the fridge and dust with powdered sugar just before serving.

More Sourdough Discard Recipes

If you enjoy clever ways to use sourdough starter discard, this is just the beginning - there are plenty more sourdough discard recipes to satisfy your sweet tooth below.