Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.
Cream the butter and sugars together for 2–3 minutes, until light and fluffy.
Add the egg and vanilla and mix until fully combined.
Whisk dry ingredients (flour, baking soda, salt) in a separate bowl.
Combine wet and dry ingredients until a soft dough forms. Fold in the sprinkles.
Scoop dough into 1½ tablespoon balls and place 2 inches apart on your baking sheet.
Chill for 20–30 minutes if your kitchen is warm (optional but helps prevent spreading).
Bake for 9–11 minutes, until the edges are just set and the centers look slightly underbaked.
Cool on the pan for 5 minutes, then transfer to a wire rack. They’ll firm up as they cool.