Preheat the oven to 350°F. Line an 8 x 8-inch square pan with foil, leaving enough overhang to use as a handle. Lightly coat the foil with non-stick spray.
In a large bowl, combine the flours, almond meal, sugar, salt and flaked coconut; stir to combine dry ingredients.
Use a pastry cutter or two knives to cut in the cubed butter, working the mixture until the butter has been reduced to pea-size crumbs. Use your hand to knead the butter into the dry mixture.
When all dry ingredients have been incorporated, press the mixture evenly into the bottom of the prepared pan.
Bake for 20 minutes, until the crust is just beginning to brown around the edges.
Lemon Custard
While the crust bakes, whisk together the sugar, eggs, lemon juice, lemon zest, flour and baking powder.
Remove the hot crust from the oven and pour the custard over the top immediately; return the pan to the oven and bake for 10 minutes.
Sprinkle the remaining 1/4 cup coconut over the custard; bake for another 8 to 10 minutes, just until the lemon topping is set at the center. (If you aren't using the coconut topping, just bake for 18 to 20 minutes, until the lemon custard is set at the center.)
Transfer the pan to a rack and let the lemon bars cool completely. Use the foil to move the bars to a work surface when you're ready to cut them. (If you're topping them with powdered sugar, now is the time.)
Assuming you have any left over, these bars can be stored in a covered container in the refrigerator for 2 or 3 days.
