Cream together the butter and shortening with an electric mixer until well blended, light and fluffy.
Add in the vanilla extract and milk.
Continue to mix until incorporated.
Gradually add in the powdered sugar mixing well after each addition until you have added in 3 cups of powdered sugar. The frosting should be soft but hold its shape in stiff peaks, if necessary add up to one more cup of sugar to get the desired texture.
Set finished frosting aside.
Decorate the Ice Cream Cones
In the bowl of a double boiler, melt the red candy melts over medium heat. If necessary to create a smooth texture, add 1-2 tablespoons of shortening.
Place parchment paper on your countertop.
Roll the cones in the melted candy melts to evenly coat the outside. Place them on the parchment paper to cool.
Frost the Cupcakes
Place the sanding sugar or white sprinkles in a shallow dish.
Add the frosting to an icing bag fitted with a round tip. Pipe the frosting onto the top of the cupcakes.
Gently dip the frosted cupcakes into the sanding sugar to coat the frosting.
Form Santa's Hat
Coat the mini marshmallows in the frosting.
Then dip it into the sanding sugar as well to coat the frosting.
Put a small dot of frosting on the tip of the ice cream cone and gently press the marshmallow into place. Repeat until all of the cones have mini marshmallows attached.
Finally gently press the ice cream cones on top of the cupcakes.
Notes
You might find it easier to place the mini marshmallows on a toothpick or bamboo skewer when frosting.
The cupcakes are best assembled right before you serve them.