Preheat your oven to 200°F (93°C) and line the baking sheet with parchment paper.
In a mixing bowl, combine the egg whites and cream of tartar. Using an electric mixer, beat on medium speed until soft peaks form.
Gradually add the granulated sugar, one tablespoon at a time, while continuing to beat on high speed until stiff peaks form and the mixture is glossy.
Gently fold in the vanilla extract and Jello mix using a spatula, being careful not to deflate the egg whites.
Spoon dollops of the meringue mixture onto the prepared baking sheet, ensuring they are spaced out as they won't spread much.
Bake in the preheated oven for about 60 minutes, or until the cookies are dry to the touch and easily lift off the parchment paper.
Once done, turn off the oven and allow the cookies to cool in the oven with the door slightly ajar for about 30 minutes to help them dry out completely.