Preheat the oven to 350 degrees.

Prepare two muffin pans with cupcake liners. Spritz the cupcake liners with nonstick cooking spray.

In a mixing bowl, whisk together the flour, sugar, brown sugar, baking powder, baking soda, and salt.

Add the melted butter and the oil to that dry ingredient mixture, beating until blended. The mixture will be thick like a cookie dough.

Beat in the peanut butter into the dough until mixed throughout.

Beat in the eggs one at a time, making sure to mix well between each addition and scrape down the sides as needed.

Next, mix in the vanilla, sour cream, and buttermilk until evenly mixed.

Using a large cookie scoop, fill the cupcake liners about ⅔ full.

Bake the cupcakes for 22 to 25 minutes or until a toothpick inserted in the middle comes out clean.

Remove the cupcakes from the oven and allow them to cool completely on a wire rack prior to frosting.

Beat together the peanut butter and the butter until creamy.

Add the confectioner’s sugar and salt, beating until the mixture is smooth.

Add the milk to the frosting, scraping down the sides, and beat until fluffy or about 1 minute.

Transfer the frosting to a piping bag and decorate the cupcakes as desired.