Preheat your oven to 350°F (175°C) and line your baking sheets with parchment paper.

In a large mixing bowl, combine softened unsalted butter and granulated sugar. Beat until light and fluffy, about 2-3 minutes.

Add in the large egg and beat until fully incorporated, about 1 minute.

In a separate bowl, whisk together all-purpose flour, baking powder, and salt. Gradually add to the wet mixture until a cohesive dough forms.

Divide the dough into 3-4 portions and mix in your chosen Jello flavor into each section.

Wrap each portion in plastic wrap and chill in the refrigerator for about 15-20 minutes.

Scoop dough and roll into balls, then roll in additional granulated sugar before placing on baking sheets.

Bake for 8-10 minutes until edges are set and tops slightly crackled.

Cool on the baking sheets for about 2 minutes, then transfer to a wire rack to cool completely.

Store in an airtight container for up to 5 days or freeze for up to 2 months.