Beat softened butter and 1½ cups powdered sugar in a large bowl until fluffy, then mix in the flour.
Divide dough into two bowls, adding yellow food coloring and lemon zest to one, and green food coloring and lime zest to the other; mix each until incorporated.
Roll 2 teaspoons of dough into balls, flatten, and place on parchment-lined baking sheets.
Bake for 6-8 minutes, until edges are just set, then cool completely.
In two small bowls, mix ½ cup powdered sugar each with the juice of one lemon and one lime to form a thick glaze.
Spoon glaze onto the center of each cookie, garnish with zest if desired, and let icing harden for an hour.
Serve and enjoy!
Notes
Use a small cookie scoop to ensure uniform cookie sizes for even baking.
Keep a close eye on the cookies while baking; they should be set around the edges but not browned.
Store cookies in an airtight container at room temperature for up to a week, or freeze for longer storage.