Preheat the oven to 375 degrees.

In a medium bowl combine the flour, baking powder, and salt. Mix and set aside.

In a large bowl cream together the butter and sugar. Add in the egg, vanilla, and lemon zest and mix until combined.

Add half the flour mixture to the butter mixture and mix until combined. Add remaining flour mixture and mix until just combined.

Roll the dough into 1 tablespoon balls and place on a baking sheet 2 inches apart. Use the bottom of a glass and flatten into a disk shape.

Bake for 8-10 minutes or until the cookies look set and the bottoms are just beginning to brown.

Remove from oven and use a teaspoon to press an indentation in the center of the cookies. Let the cookies rest for 3 minutes then remove to a wire rack to cool completely.

Fill each indentation with 1 teaspoon of key lime curd.