Step 1

Preheat the oven to 350°. Lightly grease a 9-by-9-inch square baking pan then line with parchment paper, leaving an overhang on all sides. Microwave the peanut butter for 30 seconds; stir. Repeat as necessary until peanut butter is pourable. Pour into the prepared pan. Freeze until firm, about 1 hour. Remove the peanut butter layer and transfer to a small sheet tray. Store in the freezer until ready to use.

Step 2

Sift together the flour and cocoa powder in a medium mixing bowl.

Step 3

Melt the butter and chocolate in a medium saucepan over medium heat, stirring often. Remove from heat.

Step 4

Beat the sugar, salt, vanilla, and eggs in a large bowl with an electric mixer at medium-high speed until fluffy, about 3 minutes. Slowly drizzle in the melted chocolate mixture on low speed until combined. Beat in the flour mixture on low speed until just combined.

Step 5

Pour half of the batter into the prepared pan. Remove peanut butter layer from the freezer, and place on top of brownie batter. Top with the remaining half of the brownie batter, and spread to even out the top. Sprinkle the top with the chocolate chips and peanut butter chips.

Step 6

Bake in the preheated oven for about 40 minutes or until puffed, dry to the touch, and set on the top (a wooden pick inserted in the center will not come out clean). Cool completely in the pan on a wire rack, about 3 hours. Cut into 16 squares.