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

In a medium bowl, whisk together the all-purpose flour, baking powder, and salt.

In a large mixing bowl, cream together the softened unsalted butter and powdered sugar until light and fluffy.

Gradually mix in the egg yolk, fresh key lime juice, and key lime zest until fully incorporated.

Slowly add the dry ingredients to the wet mixture and mix until just combined.

Knead the dough until it comes together, then roll into 1-inch balls and place on baking sheets.

Bake for 15-20 minutes until lightly golden around the edges but soft in the center.

Roll warm cookies in powdered sugar while still warm for coating.

Transfer cookies to a wire rack and let them cool completely.