In a medium bowl, whisk together the gluten-free flour, baking powder, and salt. Set aside.
In a large bowl using a hand mixer or a stand mixer fitted with a paddle attachment, beat the butter and granulated sugar together on medium-high speed until creamed, about 1 minute. Add the egg and vanilla extract and beat on high speed until combined, about 1 minute. Scrape down the sides and up the bottom of the bowl and beat again as needed to combine.
Add the dry ingredients to the wet ingredients and mix on low until combined. Mix in the buttermilk and sprinkles. Dough will be thick and sticky.
Scoop large sections of dough (about 2 Tablespoons of dough each) and roll into balls. Optional but delicious: Lightly dip the tops of the cookie dough balls in more sprinkles. Place dough balls onto a large plate or lined baking sheet. Cover with plastic wrap.
Chill the dough balls for at least 2 hours or up to 3 days. (Transfer to an airtight container if storing more than a few hours.)
Preheat the oven to 350F. Place the cookies 2 inches apart on a lined baking sheet. Bake for 10-12 minutes. Let sit on the baking sheet for 5 minutes then transfer to a wire rack to continue cooling. Enjoy!
IMPORTANT: This dough contains a lot of butter (which makes the cookies so delicious) but it really needs the chilling time so the butter hardens. This will prevent the cookies from spreading too much during baking.Notes on the Ingredients