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Stack of fudgy shortbread brownies with a buttery crust and swirled chocolate frosting

Decadent Chocolate Sugar Cookie Bars

These Chocolate Sugar Cookie Bars are a chocolate lover's dream, featuring a rich, fudgy cookie base topped with a silky smooth chocolate buttercream frosting. Perfect for parties, potlucks, or an everyday sweet treat!
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Prep Time 25 minutes
Cook Time 22 minutes
Total Time 47 minutes
Servings: 16 bars
Course: Dessert, Snack
Cuisine: American
Calories: 310
Ingredients Equipment Method Notes

Ingredients
  

For the Chocolate Cookie Base
  • 1 1/2 cups all-purpose flour
  • 1/2 cup unsweetened cocoa powder good quality
  • 1 tsp baking powder
  • 1/2 tsp salt
  • 1/2 cup unsalted butter 1 stick, softened to room temperature
  • 1 cup granulated sugar
  • 1 large egg room temperature
  • 1 tsp vanilla extract
For the Chocolate Buttercream Frosting
  • 2 cups powdered sugar sifted
  • 1/2 cup unsweetened cocoa powder sifted, good quality
  • 1/4 cup unsalted butter 1/2 stick, softened to room temperature
  • 3-4 tbsp milk or heavy cream, adjust as needed
  • 1/2 tsp vanilla extract
  • pinch salt

Equipment

  • 9x13 inch Baking Pan
  • Parchment Paper
  • Large Mixing Bowl
  • Electric mixer (stand or hand)
  • Medium Mixing Bowl
  • Whisk
  • Spatula
  • Measuring cups and spoons

Method
 

Prepare the Cookie Base
  1. Preheat your oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper, leaving an overhang on the sides to easily lift out the bars later. Lightly grease the parchment paper.
  2. In a medium bowl, whisk together the all-purpose flour, 1/2 cup cocoa powder, baking powder, and 1/2 tsp salt. Set aside.
  3. In a large mixing bowl, using an electric mixer, cream together the softened butter and granulated sugar until light and fluffy (about 2-3 minutes).
  4. Beat in the egg and vanilla extract until well combined and smooth, scraping down the sides of the bowl as needed.
  5. Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix; overmixing can lead to tough bars.
  6. Press the cookie dough evenly into the prepared 9x13 inch baking pan. You can use your hands (lightly floured if sticky) or a flat bottom of a glass to ensure an even layer.
  7. Bake for 20-22 minutes, or until a wooden skewer inserted into the center comes out with moist crumbs, but not wet batter. The edges should look set. Do not overbake to keep the bars soft and fudgy.
  8. Remove the pan from the oven and let the cookie base cool completely in the pan on a wire rack before frosting. This is crucial for the frosting to set properly.
Make the Chocolate Buttercream Frosting
  1. While the cookie base cools, prepare the frosting. In a medium bowl, cream the softened butter with an electric mixer until smooth.
  2. Gradually add the sifted powdered sugar and sifted cocoa powder, alternating with the milk, mixing on low speed until combined, then increase speed and beat until light and fluffy. Add the vanilla extract and pinch of salt, mixing until smooth and well incorporated. If the frosting is too thick, add more milk 1 teaspoon at a time; if too thin, add more powdered sugar.
Assemble and Serve
  1. Once the cookie base is completely cool, spread the chocolate buttercream frosting evenly over the top using an offset spatula or the back of a spoon.
  2. For cleaner cuts, chill the frosted bars in the refrigerator for at least 30 minutes before lifting them out of the pan using the parchment paper overhang. Cut into 16 squares.
  3. Serve and enjoy!

Notes

Store Chocolate Sugar Cookie Bars in an airtight container at room temperature for up to 3-4 days, or in the refrigerator for up to a week. For an extra touch, sprinkle with flaky sea salt or chocolate sprinkles before the frosting sets.