Preheat your oven to 200°F (93°C). Line a baking sheet with parchment paper.
In a mixing bowl, combine the egg whites and cream of tartar. Start mixing on low speed, gradually increasing to medium speed until soft peaks form.
Gradually add the granulated sugar, one tablespoon at a time, while continuing to mix on medium-high speed until the mixture forms stiff peaks.
Gently fold in the vanilla extract and Jello powder with a silicone spatula until fully combined, being careful not to deflate the egg whites.
Use a spoon or piping bag to dollop or pipe small mounds of the mixture onto the prepared baking sheet, leaving some space between each.
Place the baking sheet in the preheated oven and bake for approximately 1 hour, or until the cookies are dry and easily lift off the paper.
Turn off the oven and let the cookies cool in the oven for an additional 30 minutes to ensure they remain crisp.
Remove from the oven, let cool completely, and then serve or store in an airtight container.