01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - Whisk together flour, baking soda, baking powder, and salt in a medium bowl. Set aside.
03 - Beat softened butter and granulated sugar in a large bowl until light and fluffy, approximately 2 minutes.
04 - Mix in egg and vanilla extract until fully incorporated.
05 - Gradually add dry ingredients to wet mixture, mixing until just combined. Avoid overmixing.
06 - Divide dough evenly between two bowls. Add one package of Jello powder to each bowl and knead until color and flavor are evenly distributed throughout dough.
07 - Sop tablespoon-sized portions of dough, roll into balls, then coat generously in extra granulated sugar.
08 - Place sugar-coated dough balls 2 inches apart on prepared baking sheets.
09 - Bake for 8-10 minutes until edges are set but centers appear slightly underbaked for optimal chewiness.
10 - Let cookies rest on baking sheet for 5 minutes, then transfer to wire rack to cool completely.