Preheat oven to 350F, and spray an 8" cast iron skillet with nonstick spray. If you don't have a skillet, you can also use an oven safe 8x8 baking dish.

In a large bowl, mix together the sugar, cocoa, flour, salt, and baking powder.

Add in the melted butter, eggs, and vanilla, and mix well until a thick dough forms. Stir in the 2 tablespoon of creamy peanut butter.

Spread half of the brownie batter into your skillet or baking dish. Top with a layer of unwrapped Reese's cups, then spread the remaining brownie batter on top.

Drop spoonfuls of the reserved peanut butter on top, and gently swirl it into the batter. Finally, sprinkle on the Reese's mini cups.

Bake brownie in preheated oven for 25-30 minutes, until the top appears dry and a toothpick inserted in the center comes out with just a few crumbs. It's ok if the center appears a little jiggly, as it will solidify as it cools.

Let brownie come to room temperature, then enjoy!