Heat the oven to 350 °F and get your baking sheet ready. The dough bakes best when the oven is fully hot from the start, which helps the cookies set before they spread too far.

Beat the softened butter and sugar together until the mixture looks pale and fluffy. It should feel light, almost like thick frosting, which means you’ve added enough air for a tender cookie.

Add the egg and vanilla, then mix until smooth and fully blended. The mixture should look creamy and even, with no streaks of egg left behind.

Whisk the flour, baking powder, baking soda, and cream of tartar in a separate bowl. This spreads the leavening evenly so the cookies bake with a consistent texture.

Add the dry mixture to the butter mixture a little at a time and mix just until a dough forms. Stop when the flour disappears so the cookies stay soft instead of turning tough.

Divide the dough into 4 sections, then knead 2 tbsp jello powder into each section until the color is even. You’ll see streaks at first, then the dough will turn into a smooth, uniform color as soon as it’s ready.

Shape the dough into 1-inch balls and roll each one in extra jello powder or sugar. The coating adds sparkle and flavor, and extra Jello makes the color pop even more.

Set the dough balls on a baking sheet 2 inches apart and press them down gently. That slight flattening helps them bake evenly and gives them the classic sugar cookie shape.

Bake for 8 to 10 min. The cookies are done when the edges are set and the centers have lost their glossy sheen but still look a little soft.

Move the cookies to a rack and let them cool before serving. They firm up as they cool, so don’t judge the final texture straight from the pan.