In a medium bowl, whisk together the melted butter and sugar until smooth. Add the eggs and vanilla and mix until shiny and thick.
Stir in the cocoa powder, flour, salt, and baking powder.
Pour the batter into the prepared pan and smooth the top. Bake for 20–22 minutes. Let them cool completely before moving to the next layer.
While the brownies cool, beat together peanut butter, softened butter, powdered sugar, vanilla, and milk in a mixing bowl until smooth
Spread the peanut butter mixture evenly over the cooled brownie base using a spatula.
Place the pan in the fridge for about 15 minutes while you prepare the chocolate topping.
In a small microwave-safe bowl, combine chocolate chips and peanut butter. Heat in 20-second intervals, stirring after each, until melted
Pour the chocolate mixture over the chilled peanut butter layer and tilt the pan gently to spread it evenly.
Refrigerate again for 30–40 minutes
