It doesn't have to be your birthday to enjoy this brightly colored sugar cookie.
Preheat the oven to 350 degrees.
Melt butter in a heated 8-inch cast iron skillet. Whisk in sugar and vanilla. Remove from heat and allow pan to cool about 5 minutes.
Carefully whisk eggs into the sugar mixture.
In a small bowl, combine the flour, baking soda, and salt. Add the dry mixture to the skillet until just combined. Fold in white chocolate chips and sprinkles.
Bake for 15-18 minutes, or until beginning to turn golden on top and around the edges but still soft in the center. Don’t overbake. Remove from the oven and let cool for 5 minutes.
Sprinkle with extra sprinkles and top with scoops of vanilla or birthday cake ice cream or decorate with frosting, as desired.