01 -
In a large bowl, beat the butter and sugar on medium speed until pale and fluffy, about 2-3 minutes. Scrape down the bowl.
02 -
Beat in the eggs one at a time, then mix in the vanilla until smooth.
03 -
Whisk the flour, baking soda, cream of tartar, and salt in a separate bowl. Add to the butter mixture and mix on low just until no dry flour remains.
04 -
Gently fold in 1/2 cup sprinkles. Avoid overmixing so the sprinkle colors do not streak too much.
05 -
Divide the dough into 4 portions. Leave one plain, then tint the other portions pink, blue, and purple with gel food coloring.
06 -
Break the colored doughs into chunks and place them together in one bowl. Press and fold just 3-4 times so the colors marble but do not blend.
07 -
Scoop dough into 2 tablespoon balls. Roll in extra sprinkles or sugar if desired, place 2 inches apart on lined baking sheets, and chill for 20 minutes.
08 -
Heat the oven to 350°F (175°C). Bake for 10-12 minutes until the edges are set and the centers still look soft. Cool on the baking sheet for 5 minutes, then transfer to a wire rack.