Preheat the oven to 365F degrees and line 2 muffin tins with cupcake liners. You will get 18-20 cupcakes in total.
In a large bowl whisk together the flour, cocoa, baking powder, baking soda, and salt.
In a separate bowl - whisk together the oil, sugars, eggs and vanilla.
Scrape down the sides of the bowl and stir in the sour cream.
Whisk in about ½ of the flour mixture, followed by ½ of the buttermilk. Repeat the process with the rest of the flour & buttermilk.
Spoon the batter into the prepared muffin pan, filling each about ½ full.* You should get 18-20 cupcakes total.
Bake 1 pan at a time in the middle rack of the preheated oven for 17-20 minutes, or until an inserted toothpick comes out clean. Cool in the muffin pan for at least 10 minutes, then remove and continue cooling on a wire rack.
Peanut Butter Frosting
In a large bowl, beat the butter until soft.
Then add in the peanut butter and continue beating until until evenly combined.
Add in the 2 cups powdered sugar, the vanilla extract and salt and carefully beat them in with the mixer on low speed.
Beat in the rest of the powdered sugar about ½ cup at a time, alternating with the whipping cream until the desired sweetness and thickness is reached.
Frost the cupcakes using a piping bag or with the flat-edge of a knife. I frosted mine using a 1M Wilton tip.
Buttermilk, eggs and sour cream should be room temperature before making the cupcake batter.
If you don't have buttermilk, add 1 teaspoon distilled vinegar to a liquid measuring cup. Add in ½ cup milk (1% or 2%) and stir the mixture. Let it stand for 5 minutes before using.
Do not fill the cupcake liners more than ½ - ⅔ full. If you end up with 14-16 cupcakes, then they are likely too full. Otherwise, they can sink in the middle.
Make-ahead Tips: Cupcakes can be made 1 day ahead, cooled fully, and then stored in an airtight container overnight at room temperature. Frost the cupcakes the day you plan to serve. Unfrosted cupcakes can be frozen for up to 2 months in an airtight container, then thaw in the fridge and bring to room temperature before frosting and serving. Store leftovers in an airtight container at room temperature for up to 2 days, or in the fridge for up to 4 days.
Nutrition information is based on 1 cupcake, with the recipe yielding 20 cupcakes