Chocolate Peanut Butter Cake (Reese's Cake)

I made this for my brother-in-law's birthday this past weekend. I didn't eat any, but everyone said it was delicious! The hardest part was not eating all of the Reese's Cups as I made it.

Chocolate Peanut Butter Cake

Source: Amber's Delectable Delights

For the cake
2 cups all-purpose flour
1/2 cup unsweetened cocoa powder
1/2 teaspoon baking powder
1/2 teaspoon baking soda
1/2 teaspoon salt
2 sticks unsalted butter, at room temperature
1 1/2 cups sugar
2 large eggs
2 large egg yolks
1 teaspoon vanilla extract
1 cup buttermilk
4 ounces bittersweet chocolate, melted and cooled (optional)

For decorating
1 ½ – 2 batches peanut butter frosting
Miniature Reese’s cups, halved and/or chopped (I put them in the freezer for about half an hour to make it easier to cut)

Directions
1. For the cake, center a rack in the oven and preheat the oven to 350°. Butter two 9×2” round cake pans, dust the insides with flour, tap out the excess and line the bottoms with rounds of parchment paper. Place the pans on a baking sheet.
2. In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda and salt. Set aside.
3. In a stand mixer fitted with the paddle attachment, beat the butter on medium speed until soft and creamy. Add the sugar and beat for about 2 minutes, until thoroughly blended into the butter. Add the eggs and yolks one at a time, beating for one minute after each addition and scraping down the sides of the bowl as needed. Beat in the vanilla. Reduce the mixer speed to low and add the dry ingredients alternately with the buttermilk; add the dry ingredients in 3 additions and the buttermilk in 2 (beginning and ending with the dry ingredients). Mix each addition only until it is blended into the batter. Scrape down the bowl and add the melted chocolate, if using, folding it in with a spatula. Divide the batter between the prepared cake pans. 4. Bake for 26-30 minutes or until the cakes feel springy to the touch and start to pull away from the sides of the pans. Transfer to wire racks to cool for about 5 minutes, then run a knife around the sides of the cakes, unmold them and peel off the paper liners. Invert and cool to room temperature right side up.
5. To assemble the cake, place one cake layer on a cardboard circle covered in foil. Spread peanut butter frosting on top of the cake layer. (If desired, sprinkle with chopped Reese’s cups.) Place the second cake layer on top of the frosting. Frost the top and outside of the cake with remaining peanut butter frosting. Decorate with halved and chopped Reese’s cups as desired.