I like to think that, on good days, each of us is filled to the brim with happiness, color, and confetti. Now, thanks to this cookie from Joy Wilson’s book, Homemade Decadence, we can eat exactly how we feel.
In a medium bowl, whisk together the flour, baking powder, cream of tartar, baking soda, and salt.
In the bowl of an electric mixer fitted with the paddle attachment, beat the butter and sugar at medium speed until light and fluffy, 3 to 4 minutes. Split the vanilla bean and scrape the seeds into the bowl. Add the egg and vanilla extract, and beat until thoroughly combined.
Reduce the mixer speed to low, and slowly add the dry ingredients to the wet ingredients. The dough will be thick (you may have to finish incorporating the mixture with a spatula). Fold in ¼ cup of the sprinkles.
Put the remaining ¼ cup sprinkles in a bowl. Scoop up 2 tablespoons of dough and roll it into a ball. Dip the ball into the bowl of sprinkles to cover lightly. Put the ball on a plate. Repeat with the remaining sprinkles and dough, and chill for at least 2 hours.
Put racks in the center and upper third of the oven and preheat the oven to 350 degrees. Line 2 large baking sheets with parchment paper.
Transfer the chilled dough balls to the prepared baking sheets, leaving about 2 inches of space in between each ball.
Bake until the cookies have spread and are just beginning to brown around the edges, but are mostly pale and soft, 8 to 10 minutes. Let cool on the cookie sheets for 5 minutes before transferring to wire racks to cool completely. The cookies will keep in an airtight container for up to 4 days.