Preheat the oven to 350℉. Prepare muffin tins with 18 cupcake liners or grease with non-stick spray.

In a large bowl, whisk together the melted butter, oil, sugar, vanilla, vinegar, and eggs until well combined. Add the sour cream and milk and whisk until incorporated.

In another bowl, whisk together the flour, cocoa powder, baking soda, baking powder, and salt. Sift the dry ingredient mixture through a wire sieve into the bowl with the combined wet ingredients and stir just until no streaks or clumps of flour remain. Do not overmix!

Distribute the batter evenly between the 18 cupcake liners in the prepared pans, filling each liner about ½ full. Bake in the preheated oven for 15-18 minutes or until a toothpick inserted into the center comes out clean. Let cool in the pans for 10 minutes before transferring to a wire rack to cool completely before frosting.

In a large bowl, cream together the softened butter and sifted cocoa using an electric handheld mixer on medium-high speed. Add the powdered sugar, 1 cup at a time, mixing on low between each addition. Add 2-3 tablespoons of milk and beat the frosting at high speed until fluffy.

Frost the fully cooled cupcakes using a piping bag fitted with your desired tip. Sprinkle with chocolate shavings, if using. Enjoy!