1. Preheat oven to 350 degrees and line pans with cupcake liners.

2. Sift cake mix to remove lumps and set aside.

3. In a large bowl, combine eggs, oil, milk, sour cream and vanilla extract.

4. Add cake mix and stir until smooth.

5. Fill cupcake liners 3/4 full and bake for 17-22 minute or until an inserted knife will comes out clean.

6. Buttercream: Beat butter for two minutes. Add vanilla extract, cocoa powder and milk and beat again. Slowly add powdered sugar until you reach your desired consistency.

7. Pipe onto cooled cupcakes and top with sprinkles.