Sourdough Sugar Cookie Bars

These frosted sourdough sugar cookie bars are a fun, easy treat made with simple pantry staples and a touch of sourdough tang. They’re soft, buttery, and topped with a thick layer of creamy frosting—perfect for decorating with sprinkles, colored frosting, or leaving plain for a more classic vibe. Whether you’re baking for a celebration or just want something sweet and nostalgic, these bars are endlessly customizable and always a hit.

What makes these sourdough sugar cookie bars stand out?

• Depth of flavor: The sourdough starter adds a subtle tang that makes the flavor more complex and irresistible.

• Texture: They’re soft, thick, and perfectly chewy—like the best parts of a sugar cookie in bar form.
  
• Crowd pleaser: A fun, easy way to use up sourdough discard in a crowd-pleasing dessert.

• Convenience: Stay moist and tender for days, making them great for make-ahead treats.

Tips for Success

• Cool Completely: Allow the cookie bars to cool completely in the pan before cutting to prevent them from falling apart.

• Room Temperature Ingredients: Use room temperature ingredients to ensure even mixing and a smooth batter.

• Measure Accurately: Weigh your ingredients for precise measurements, especially the flour and sugar, to achieve the desired consistency.

• Sourdough discard: I recommend using discard no more than a week old as this may result in a sour result.

• Do Not Overmix: Mix the batter just until combined to avoid developing too much gluten, which can result in tough cookie bars.

How to make sourdough cookie bars: step-by-step

INGREDIENTS

• 113 grams unsalted butter (softened)
• 150 grams of sugar
• 1 large egg
• 100 grams of sourdough starter (fed or unfed & brought to room temp)
• 7 grams vanilla extract
• 140 grams of all-purpose flour
• 3 grams of baking powder
• 2 grams of salt
• 1 teaspoon cornstarch
• 80 grams of rainbow sprinkles

For the frosting:

• 2 tablespoons of unsalted butter (softened)
• 1 1/2 cups powdered sugar
• 2-3 tablespoons of heavy cream
• 1 teaspoon vanilla extract
• 1 drop of red food dye (for pink color-optional)
• a pinch of salt to cut the sweetness (optional)

Equipment

• 1 metal 9×9-inch baking pan (8×8 inch works too)
• parchment paper
• food scale
• mixing bowl
• hand mixer or stand mixer

Instructions

• Preheat the oven to 350°F (175°C). Line a 9×9 inch (or 8×8-inch) baking pan with parchment paper.

• Cream the butter and sugar together in a large bowl until light and fluffy (about 2–3 minutes). You can use a hand mixer or stand mixer for this step.

• Add the egg, sourdough starter, and vanilla extract to the bowl. Mix until well combined and smooth.

• In a separate bowl, whisk together the flour, baking powder, salt, and cornstarch.

• Gradually mix the dry ingredients into the wet mixture, stirring just until combined. Be careful not to overmix.

• Fold in the sprinkles using a spatula, making sure they’re evenly distributed throughout the dough.

• Spread the dough evenly into the prepared baking pan. Use a spatula or your hands to press it into the corners and smooth the top. Note: this is a wetter sugar cookie bar dough, this is normal. It helps achieve optimal texture.

• Bake for 28-35 minutes, or until the edges are lightly golden and a toothpick inserted into the center comes out clean. Note: if using an 8×8 inch pan you may need to bake the sugar cookie bars a little longer.

• Let the bars cool completely in the pan before frosting.

How to make the frosting

• In a medium bowl, beat the softened butter until smooth.

• Add the powdered sugar, 2 tablespoons of heavy cream, vanilla extract, 1 drop of red food dye, and a pinch of salt (if using). Beat until smooth and fluffy. Add the remaining tablespoon of cream if needed to reach your desired consistency.

• Spread the frosting over the cooled bars, then top with extra sprinkles if you’d like.

• Slice into squares and enjoy!

• Store the frosted bars in an airtight container at room temperature for up to 2 days, or refrigerate for up to 5 days for maximum freshness.

More sourdough dessert recipes

• Sourdough Blondies
• Sourdough Brownies
• Sourdough Discard Cinnamon Roll Muffins
• Sourdough Blueberry Bread