Make the Bars:

Preheat Oven:

Preheat to 350°F (175°C).

Grease or line a 9x13-inch baking dish with parchment paper.

Cream Butter & Sugars:

In a large bowl, beat together butter, peanut butter, granulated sugar, and brown sugar until light and fluffy.

Add Eggs & Vanilla:

Beat in the eggs and vanilla until well combined.

Add Dry Ingredients:

In a separate bowl, whisk together flour, baking powder, and salt.

Gradually add to the wet ingredients and mix until just combined.

Bake:

Spread the dough evenly into the prepared pan.

Bake for 22–25 minutes, or until the edges are lightly golden and a toothpick comes out clean.

Do not overbake—the bars should stay soft.

Make the Frosting:

Heat & Mix:

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

Stir in milk and vanilla, then whisk in powdered sugar until smooth.

Frost While Warm:

Spread the frosting over the bars while they’re still warm so it melts slightly into the top.

Let cool completely before slicing into bars.