Preheat the oven to 375 degrees. Grease a 9 by 15-inch baking sheet and set aside. In a large bowl, toss together the almonds, cornmeal, sugar, and cake flour. Make a well in the center of these dry ingredients and add the egg yolks, vanilla, and lemon and orange zests. Use a fork to incorporate the wet ingredients into the dry ingredients. With your hands, rub the butter into the dry mixture to form a crumbly dough. Shake the dough out onto the prepared baking sheet, spreading to distribute it evenly. Pat it down. Bake until golden brown and firm, about 25 minutes. Allow to cool, and serve. Or break into small pieces and store in an airtight container for up to 1 week.