Preheat your oven to 350°F (175°C). Line your cupcake pan with cupcake liners to make for easy removal later.
In a large mixing bowl, combine the devil's food cake mix and the chocolate pudding mix. Whisk them together until they are well blended.
Add the sour cream, vegetable oil, eggs, milk, and vanilla extract to the dry ingredients. Using an electric mixer, beat the mixture on medium speed for about 2 minutes until the batter is smooth and well combined.
Scoop the batter into the prepared cupcake liners, filling each about two-thirds full.
Place the cupcake pan in the preheated oven and bake for 18-20 minutes, or until a toothpick inserted into the center of a cupcake comes out clean.
Once baked, remove the cupcakes from the oven and allow them to cool in the pan for about 5 minutes. Then, transfer them to a wire rack to cool completely.
In a large mixing bowl, beat the room temperature butter with an electric mixer until smooth and creamy. Gradually add the powdered sugar, alternating with the whipping cream and vanilla extract. Beat on low speed until combined, and then increase to medium speed until the frosting is fluffy and spreadable.
Once the cupcakes are completely cool, use a piping bag or spatula to generously frost each cupcake with the buttercream.
