Using a stand or hand mixer, beat the butter and sugar together for a few minutes until they are light and fluffy, it will depend on your mixer’s motor.
Next, add your egg and vanilla extract and beat until combined, no need to beat excessively.
In a separate bowl whisk together flour, baking powder, baking soda, and cream of tartar.
With the mixer on low, slowly add the flour mixture, making sure to turn off the mixer to scrape the bowl a few times to get everything mixed together. Also, make sure not to overmix, once you can no longer see flour you are good.
Remove bowl from mixer and fold in the sprinkles by hand using a wooden spoon or spatula.
Using a 2 teaspoon scooper (or whatever size you want) scoop out the dough onto a prepared cookie sheet, I like to line my cookie sheets with parchment or a Silpat. Pop the cookie sheet (with dough) into the freezer for at least an hour or up to 3 days. This will help with spreading.
When you are ready to bake, take the dough out of the freezer and preheat the oven to 350°F. This will give the dough a little time to come to room temp (or at least a little closer to room temp).
Once the oven is ready, take a few balls of dough and place them on their own cookie sheet with about 2 inches in between each one, then bake for 12-13 minutes. I like to rotate my cookies halfway through because my oven definitely has some hot spots and this ensures even baking.
Remove cookies from the oven when the edges begin to get golden brown. Cookies will puff up a bit at the end of baking but once cooled will flatten out. Let the cookies cool on the baking sheet for about 5 minutes before transferring to a cooling rack.
Once cool, they are ready to enjoy!
These keep well in an airtight container at room temp for about a week (if they last that long without being eaten) or for a few months in the freezer in a freezer-safe container.