Preheat oven to 350 and line cupcake pan with the liners
Using a hand mixer, beat together the cake mix, butter, milk, and vanilla and mix until combined
Take a medium ice cream scoop and, scoop the batter into the cupcake liners and fill about 3/4 of the way full
Bake in the oven for about 21 minutes
Pull cupcakes out and place on the side to cool
In a standing mixer, combine the butter, powder sugar, vanilla, and the heavy whipping cream.
Mix on medium speed until stiff and creamy.
If you still see powdery pebbles, add in 2 more tbsp heavy whipping cream.
Continue to mix until stiff and creamy
Scoop frosting into the piping bag fitting with the number 3 tip
Using your tip with the frosting, pipe squiggles all over the top of the cupcake
Sprinkle the Christmas sprinkles and M&M's all over the top
Top with 4 mini marshmallows