In a medium mixing bowl, stir together the almond flour, coconut flour, sugar, baking powder and salt. Set aside.

In another medium mixing bowl, stir together the melted butter, egg, lemon zest, and lemon extract.

Add the dry mixture to the wet and stir just until combined. The dough will feel quite wet. Let it sit for 10 minutes to allow the coconut flour to absorb the liquid while the oven preheats.

Preheat the oven to 350 degrees F and line a cookie sheet with a piece of parchment paper.

Roll the dough into 1" balls and place 2" apart on the prepared cookie sheet. The dough will feel quite greasy.

Bake the cookies for 6 minutes and remove from the oven.

Using the rounded part of a 1/2 teaspoon measuring spoon, make an indentation about 3/4 of the way down into each cookie.

Fill each indentation with 1/2 teaspoon of lemon curd. Be sure not to overfill them.

Return the pan to the oven and bake for another 5-7 minutes or until the cookies feel like they have a firm outer layer. The cookies shouldn't brown around the edges - just on the bottom.

Let the cookies, which will be very soft at this point, cool for 5 minutes on the baking sheet and then remove to a wire rack to cool completely. The parchment paper may be a little greasy, but the cookies will not be.

Refrigerate in an airtight container for up to 4 days. Dust with powdered sugar before serving, if desired.