Position racks in the upper and lower thirds of the oven and preheat the oven to 350 degrees F. Line two rimmed baking sheets with parchment paper.
Cream the butter, sugar and brown sugar in the bowl of a stand mixer fitted with the paddle attachment (or with an electric hand mixer), until light and fluffy, 3 to 4 minutes.
Add the eggs and mix on medium speed to combine, then scrape the bowl well. Beat in the vanilla on medium speed.
Whisk together the flour, baking powder and salt in a medium bowl. Add about half of the flour mixture to the bowl of the stand mixer and mix on low speed to combine. Scrape the bowl well, then add the remaining flour mixture and mix on low speed to combine.
Scoop the dough into 1/4-cup mounds. Place the sprinkles in a shallow bowl. Roll the balls of dough fully in the sprinkles and transfer to the prepared baking sheets, staggering the rows of cookies to allow them room to spread during baking. Gently press each cookie with your fingers to flatten.
Bake, switching the baking sheets halfway through and rotating them from front to back, until the cookies spread and are lightly golden around the edges, 10 to 12 minutes.
Let cool 5 minutes on the baking sheets, then transfer to racks to cool completely.
You can use one kind of sprinkles or make a fun homemade blend of sprinkles with sanding sugar, jimmies and nonpareils.