Preheat the oven to 410°F/210°C and line a muffin pan with paper liners.
In a bowl, combine the all-purpose flour, cake flour, baking powder, baking soda, salt, and set aside.
In a large bowl, cream together the unsalted butter and sugar. Add the eggs one at a time, and then the sour cream and vanilla extract. Stir until combined.
In a small bowl, toss the peanut butter cups in a couple spoonfuls of the dry mixture. Set aside.
Add the dry ingredients into the wet ingredients and stir until almost completely combined. Add the peanut butter cups and fold the batter until the peanut butter cups are spread evenly throughout the batter.
Divide the batter evenly among the 12 muffin wells.
Bake at 410°F/210°C for 5 minutes, then turn down the temperature to 374°F/190°C and bake for an additional 15 minutes.
Cool in the pan for a couple minutes before taking them out onto a wire rack to cool completely.