Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a large mixing bowl, beat the unsalted butter and granulated sugar until light and fluffy, about 3-5 minutes.

Add the large eggs and vanilla extract, mixing on low speed until fully incorporated, about 2 minutes.

Whisk together the flour, baking soda, cream of tartar, and salt in a separate bowl. Gradually add to the wet ingredients, mixing on low until just combined.

Fold in the sprinkles until evenly distributed.

Divide the dough into four portions, color three portions with gel colors, and leave one uncolored.

Gently swirl the colored doughs together, being careful not to overmix.

Roll the dough into small balls, about 1-2 inches in diameter. Optional: roll in additional sugar or sprinkles.

Place on the prepared baking sheet, spacing them about 2 inches apart. Bake for 10-12 minutes until edges are lightly golden.

Let them cool on the baking sheet for a few minutes before transferring to a wire rack.

Enjoy your colorful Unicorn Cookies!