Step 1: Preheat your oven to 350°F (175°C). This ensures that your cupcakes bake evenly.
Step 2: Line your muffin tin with cupcake liners for easy removal.
Step 3: In a large mixing bowl, combine the devil's food cake mix and the Jello instant chocolate pudding mix. Mix in the sour cream, vegetable oil, eggs, milk, and vanilla extract. Beat on medium speed for 2-3 minutes until smooth and well combined.
Step 4: Pour the batter into the cupcake liners, filling each about two-thirds full.
Step 5: Bake for 18-22 minutes, or until a toothpick inserted comes out clean. Keep an eye on them towards the end.
Step 6: Remove from the oven and let cool in the tin for 5 minutes, then transfer to a cooling rack.
Step 7: For the frosting, beat the room temperature butter until creamy. Gradually add the powdered sugar, then the whipping cream and vanilla extract. Beat on high until light and fluffy, about 3-5 minutes.
Step 8: Once cupcakes are cooled, frost each with the buttercream using a piping bag or spatula.