Heat the oven to 350°F. Line a large baking sheet with parchment paper.
In a large bowl, beat the softened butter and sugar for 2 minutes, until pale and creamy. Beat in the egg and vanilla until smooth.
In a separate bowl, whisk the flour, baking powder and salt. Add to the butter mixture and stir just until no dry flour remains, then fold in the sprinkles.
Scoop 1-tablespoon portions of dough, roll lightly between your palms and set 2 inches apart on the prepared sheet, about 20 cookies.
Bake 10-12 minutes, until the edges are set and the centers still look slightly underbaked.
Cool on the sheet for 5 minutes, then transfer the cookies to a wire rack to cool completely.
