Cream the butter and cream cheese until smooth.

Add the egg and vanilla, mixing just until combined.

Beat in the cake mix until the dough is fully blended.

Stir in 1/4 cup of the sprinkles.

Refrigerate the dough for at least 1 hour or overnight.

Preheat the oven to 350 degrees. Lightly grease a cookie sheet or line it with parchment paper.

Scoop rounded tablespoons of dough and roll each into a 1-inch ball.

Sprinkle the tops with some of the remaining sprinkles, then roll each ball in confectioner’s sugar until fully coated.

Place the dough balls about 2 inches apart on the prepared cookie sheet.

Bake for 8 to 10 minutes. Let the cookies rest on the sheet for 2 minutes, then transfer them to a wire rack to cool completely.