Preheat oven to 350 degrees F. Line 24 cupcake tins with liners.
To prepare cupcakes place the cake mix, pudding mix, eggs, oil, milk and sour cream into stand mixer. Beat until well combined, about 1 1/2 minutes.
Scoop batter evenly into 24 cupcake liners.
Bake for 20-25 minutes or until cupcakes are cooked through, a toothpick comes clean from center. Remove and let cool.
Mousse
To prepare mousse, whip heavy cream with a stand or electric mixer until looks like whipped cream, until stiff peaks form.
Gently fold in melted chocolate that has cooled for 5 minutes.
Continue folding until well combined then transfer batches into a piping bag.
When cupcakes have cooled press the tip of the piping bag into the center of the cupcake about 1 inch then press mousse into center. It doesn’t take much, just one firm squeeze is perfect. Continue filling all the cupcakes.
Frosting
To prepare frosting, beat the butter, powdered sugar, cocoa and vanilla until well combined and a nice frosting consistency.
Spread over cupcakes then top with chopped Snickers.