Let's cook.
Line an 8x8 inch baking pan with parchment paper, leaving an overhang on the sides to easily lift the bars out later.
In a large bowl, combine the creamy peanut butter, 1/2 cup melted unsalted butter, powdered sugar, and vanilla extract. Mix until well combined and a thick dough forms.
Press the peanut butter mixture evenly into the prepared baking pan. Use the back of a spoon or your hands to create a smooth, compact layer.
In a microwave-safe bowl, combine the semi-sweet chocolate chips and 2 tablespoons of unsalted butter. Microwave in 30-second intervals, stirring after each, until the chocolate is melted and smooth. This usually takes 1-2 minutes.
Pour the melted chocolate mixture over the peanut butter layer in the pan, spreading it evenly with a spatula.
Refrigerate the pan for at least 2 hours, or until the chocolate topping is firm.
Once firm, use the parchment paper overhang to lift the entire slab out of the pan. Cut into 12 squares or bars and serve.
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