Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper or a silicone mat.
In a large mixing bowl, beat together the softened butter and ¾ cup sugar until light and fluffy.
Stir in the lime Jello powder (remembering to keep 1 tablespoon aside for later!).
Mix in the eggs one at a time, ensuring each is fully blended before adding the next.
In a separate bowl, whisk together the flour, baking powder, and salt.
Slowly add the dry flour mixture to the wet ingredients, mixing on low speed until just combined to form a soft dough.
Scoop the dough into small balls (a cookie scoop works great!). Roll each ball in the ¼ cup of granulated sugar to coat it evenly.
Place the coated dough balls on your prepared baking sheet. Gently press down on each cookie with the bottom of a glass to flatten slightly. Bake for 9-11 minutes, until the edges are just set but the centers still look a little soft.
Take the cookies out of the oven and let them cool on the baking sheet for 3-5 minutes before transferring them to a wire rack to cool completely.
While the cookies cool, prepare the frosting! Beat together the softened butter, cream cheese, and powdered sugar until smooth. Gradually add the milk, mixing until you reach your desired consistency. Finally, mix in the reserved 1 tablespoon of lime Jello powder until the frosting is smooth and vibrant.
Once the cookies are completely cool, spread a generous amount of the zesty lime frosting on top. Enjoy your delightful and colorful treats!