Soft-Baked Funfetti Sugar Cookies (adapted slightly from Sally's Baking Addiction)
1/2 cup unsalted butter, room temperature
3/4 cup granulated sugar
1 large egg, room temperature
1 tsp vanilla
1 and 1/2 cups all-purpose flour
1/4 tsp salt
1 tsp baking powder
1/2 tsp baking soda
1 tsp cream of tartar
1/2 cup sprinkles
Beat the softened butter until smooth, about a minute. Add the sugar and beat until pale and fluffy. This may take a few minutes. Add the egg and vanilla and beat until combined, scraping down the sides of the bowl as needed.
In a separate bowl, whisk together the flour, salt, baking powder, baking soda, and cream of tartar. Slowly add the dry ingredients to the butter and sugar mixture. Add the sprinkles and mix until just combined.
Divide the dough into 16 small balls. Place on lined (or greased) baking sheet and refrigerate for at least an hour. (This will help the cookies stay thick, instead of spreading in the oven, but you can skip it if you want)
Preheat oven to 350 degrees. Bake chilled cookie dough for 8-10 minutes, until they no longer look like mounds, but have no begun to brown. They will still look undone, leave them on the cookie sheet for three minutes, then move to a wire rack to finish cooling. (They'll stay soft if stored in an airtight container)