1. Preheat the oven to 350°F and grease or line a 9×13-inch baking dish with parchment paper.

2. In a large bowl, cream together the butter, granulated sugar, and brown sugar until fluffy.

3. Add in the eggs, one at a time, then mix in vanilla extract and creamy peanut butter until smooth.

4. Stir in flour, baking powder, and salt until just combined—avoid overmixing.

5. Pour the batter into the baking dish and spread evenly.

6. Bake for 20–25 minutes or until edges are golden and a toothpick comes out clean.

7. Let bars cool completely in the pan before frosting.

8. In a saucepan, melt the butter and peanut butter together over medium heat.

9. Remove from heat and stir in the milk.

10. Whisk in powdered sugar gradually until a thick, pourable frosting forms.

11. Spread warm frosting over the cooled bars and let it set.

12. Slice into squares once the frosting is firm.