Mix together sugar and flour, then cut butter into small pieces and work into sugar and flour with your fingers to make coarse crumbs. Put half the crumbs in the bottom of a 9" greased baking dish. Stir in egg and nutmeg to remaining crumbs. Mix sour cream with soda and add to crumb mixture. Spoon batter into dish and top with nuts. Bake in a preheated 350 degree oven for 35 to 40 minutes.