Preheat oven to 350°. Line two muffin pans with cupcake liners. (I got 18 cupcakes.)
Mix cake mix, water, oil, and eggs in a large bowl with a hand mixer for about 2 minutes. Add pumpkin and mix until combined. Fill cupcake liners about 2/3 full (I use an ice cream scoop for this).
Bake 18-22 minutes, until a toothpick insterted comes out with just a few little crumbs sticking to it. Cool completely before frosting.
To make your frosting, beat butter with mixer (hand or stand, your choice) until creamy. Slowly beat in powdered sugar (1 cup at a time). Beat in vanilla. Add 1 tablespoon of cream and mix, then add more cream as necessary to get the consistency you want. Tint with food coloring, if desired.
Frost cupcakes and sprinkle with (or dip in) sprinkles. Enjoy!
Want a fall-like cupcake that tastes like pumpkin? Add 2 teaspoons pumpkin pie spice to the cupcake batter.