Whisk together gluten-free flour, baking powder, and salt in a medium bowl.

In a large bowl, cream butter and sugar with a mixer for about 1 minute. Add egg and vanilla, beating until combined, then scrape the bowl and beat again.

Gradually add dry ingredients to wet, mixing on low until combined, then stir in buttermilk and sprinkles. The dough will be thick and sticky.

Scoop about 2 Tablespoons of dough per cookie, roll into balls, and optionally dip tops in extra sprinkles. Place on a plate or lined baking sheet and cover with plastic wrap.

Chill the dough balls for a minimum of 2 hours, or up to 3 days in an airtight container.

Preheat oven to 350F. Bake cookies 2 inches apart on a lined sheet for 10-12 minutes. Let them cool on the baking sheet for 5 minutes before transferring to a wire rack.