Chocolate Peanut Butter Bars

Preparation

1. Step 1

   Heat oven to 350 degrees. Melt butter in the microwave for about 45 seconds, or in a small saucepan over medium heat; cool for 5 minutes. Meanwhile, line a 9-by-13-inch baking pan with two pieces of parchment, creating a sling that hangs over the sides, and coat with nonstick spray.

2. Step 2

   In a medium bowl, whisk together flour, cocoa powder, baking powder, baking soda and salt.

3. Step 3

   In a large bowl, using a hand mixer, beat the peanut butter, brown sugar, granulated sugar and butter on medium speed until smooth, 1 to 2 minutes. Add the eggs, one at a time, beating until incorporated. Beat in the vanilla. (Alternatively, combine all the wet ingredients, in the same order, in a stand mixer fitted with the paddle attachment.)

4. Step 4

   Slowly add the flour mixture to the peanut butter mixture, beating on low speed until no streaks of flour remain. Use a silicone spatula to fold in Reese’s Pieces and chocolate chunks.

5. Step 5

   Transfer the dough to the prepared pan and firmly press into an even layer. Bake until puffed and a toothpick inserted comes out with just a few crumbs, 24 to 26 minutes.

6. Step 6

   Place the pan on a wire rack and cool for at least 2 hours. (The bars need to firm up before slicing or they’ll crumble.) Using the parchment sling, transfer to a cutting board and, with a sharp knife, slice into 24 bars. Serve immediately, or transfer to an airtight container and store at room temperature or refrigerate for up to 5 days.