Preheat your oven to 350°F (175°C) and prepare a 12-cup muffin tin with paper liners.

In a large mixing bowl, sift together the dry ingredients: flour, sugar, cocoa powder, baking powder, baking soda, and salt.

In another bowl, whisk together the wet ingredients: vegetable oil, buttermilk, eggs, and vanilla extract, then combine with the dry ingredients.

Fill each cupcake liner about two-thirds full with batter.

Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.

Let the cupcakes cool in the pan for about 5 minutes before transferring to a wire rack.

Prepare the peanut butter filling by beating together peanut butter, powdered sugar, and milk until fluffy and smooth.

Once cooled, cut a small hole in the center of each cupcake, fill with peanut butter mixture, and replace the tops.

Melt chocolate chips for the frosting and drizzle over the filled cupcakes.

Garnish each frosted cupcake with a mini peanut butter cup.