Preheat oven to 350° F. grease an 8" square pan, or line with parchment if you want "pretty" lemon squares.
To softened butter or coconut oil, add 1-2 T honey, 1/2 C coconut flour, and vanilla. (Or use lemon extract or an additional teaspoon or two of lemon zest, or both.) Mix well and pat evenly into prepared pan, wetting hands with cool water if it is too sticky.
Bake 10-15 minutes at 350° F while you prepare the lemon filling.
For the filling, beat eggs, lemon juice, lemon zest, baking soda, and coconut flour for about three minutes. It will be lighter yellow and a little foamy.
When the crust has begin to turn brown at the edges, remove from oven, pour the lemon filling over it, and bake another 25-30 minutes until the filling is set and doesn't jiggle anymore. It will turn a bit brown.
Cool completely before serving, and store leftovers in the refrigerator for a day or two.