Preheat oven to 425~. In a food processor or large bowl,mix 1 1/2 cups of the cornmeal with the flour, salt, sugar, cayenne pepper,baking powder and baking soda. Cut the butter into the dry ingredients until the whole mixture is the texture of cornmeal. Seperately mix the egg with the buttermilk,and stir all but 2 tbs.of this liquid into the dry mixture. Mix just enough to make a uniformly moistened dough. Dust a clean board with half the remaining cornmeal,and turn the dough out onto the floured surface.Sprinkle the top with the remaining cornmeal,and with flowered hands,gently push the dough into a circle about a 1/2" thick. Cut with a 2" or 3" biscuit cutter,and place bbiscuits close together on a greased cookie sheet.Brush top of the biscuits with the reserved buttermilk egg mixture.Bake in the preheated oven until puffed and brown,about 12 minutes.Cool for a few minutes before serving.Yields about 1 dozen biscuits.