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

Cream together 1 cup of butter, ¾ cup of granulated sugar, and ¼ cup of brown sugar for 3-4 minutes until light and fluffy.

Add 1 egg and the zest of 2-3 key limes, mixing until combined.

In a separate bowl, whisk together 2 cups of flour, ½ teaspoon of baking powder, and ½ teaspoon of salt.

Gradually stir the dry ingredients into the wet, mixing on low speed until just combined.

Shape the dough into balls and place them on the prepared baking sheets, flattening slightly.

Bake for 8-10 minutes until the bottoms are golden.

Let the cookies cool for 2 minutes on the baking sheet before transferring to a wire rack.

Whisk together 1 cup of powdered sugar, 2 tablespoons of lime juice, 2 tablespoons of heavy cream, and 1 tablespoon of rum until smooth.

Dip the cooled cookies into the glaze and return them to the wire rack to drip off excess.

Zest additional key limes over the glazed cookies before serving.