Preheat oven to 350°F and line an 8×8-inch pan with parchment paper. Mix melted butter and brown sugar until smooth. Add egg and vanilla and mix well. Stir in flour, baking powder, and salt. Spread batter into the pan and bake 18–22 minutes until set. Cool completely. Spread peanut butter over the blondie base. Melt chocolate chips and pour over peanut butter layer. Spread evenly and refrigerate 30 minutes until chocolate sets. Slice and serve.
Notes
Allow blondies to cool fully before adding peanut butter and chocolate layers to prevent melting.