Preheat oven to 350 F. In a large bowl, whisk together flour, sugar, cocoa powder, salt, and baking powder. Add in eggs, melted butter, and vanilla extract. Whisk until smooth.
Evenly divide batter between 12 greased muffin cups. Bake for 20-25 minutes. Remove from oven, place one peanut butter cup on each brownie.