Preheat the oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking dish.

Combine brownie mix, oil, water, and eggs together in a bowl until smooth; pour into the prepared baking dish.

Bake in the preheated oven until edges have started to pull away from the sides of pan, 28 to 31 minutes. Let brownies cool.

Beat confectioners’ sugar, peanut butter, and 1/2 cup butter together in a bowl until smooth and creamy; spread over cooled brownies.

Heat chocolate chips and 6 tablespoons butter together in a saucepan over low heat, stirring occasionally, until melted, about 5 minutes; spread over peanut butter layer. Cool and cut into squares.