Preheat oven to 350°F and line 2-3 baking sheets with parchment paper.

In a large bowl, beat the butter and 1 cup of granulated sugar with an electric mixer on medium speed until light and fluffy.

Reduce the speed to low and beat in the egg, yolk, and vanilla extract until well combined.

In a separate bowl, whisk the flour, baking powder, baking soda, and cream of tartar.

Gradually add the flour mixture to the butter mixture, mixing on low speed until a soft dough forms.

Divide the dough into 4 equal portions (one for each color of jello mix).

Knead 1 package of jello mix into each portion until the color is evenly distributed.

Wrap in plastic and chill for 30-60 minutes.

Portion the dough into 2 tablespoon-sized balls, or combine small amounts of each color to form larger balls.

Roll each ball in the remaining granulated sugar for a sweet coating.

Place the cookie dough balls on the prepared baking sheets about 2 inches apart.

Using the bottom of a glass, flatten each ball slightly.

Bake for 10-12 minutes or until the edges are lightly browned.

Allow to cool on the baking sheets for 5 minutes before transferring to a wire rack to cool completely.