Preheat your oven to 225°F (110°C) and line two baking sheets with parchment paper or silicone mats.

In a large mixing bowl, combine egg whites and cream of tartar. Beat on medium speed until soft peaks form, about 2-3 minutes.

Gradually add granulated sugar, one tablespoon at a time, increasing the speed to high until stiff, glossy peaks form, about 4-5 minutes.

Sprinkle in Jello powder and gently fold it into the meringue using a rubber spatula until completely blended.

Transfer the meringue into a piping bag fitted with a star tip, or use a spoon to scoop mounds onto baking sheets.

Bake for 1.5 to 2 hours until the cookies are dry to the touch and easily lift off the parchment.

Turn off the oven and leave the cookies inside for an additional hour to cool.

Gently transfer cooled cookies to an airtight container for storage.