In a large bowl, combine the softened butter and peanut butter. Beat together until smooth.

Gradually add the powdered sugar, mixing on low speed to prevent a sugar cloud.

Add the milk and vanilla extract, then beat on medium speed until the frosting is light and fluffy.

If the frosting is too thick, add more milk, one tablespoon at a time.

Taste and adjust sweetness by adding more powdered sugar if desired.

Scrape down the sides of the bowl to ensure everything is mixed well.

Use immediately or store in the refrigerator until ready to use.

Before using chilled frosting, let it sit at room temperature for 10-15 minutes to soften.

Frost your cooled cupcakes or cake with a piping bag or spatula for a beautiful finish.