Melt butter in skillet. Add onion. Saute until tender. Stir together flour, baking powder and salt. Blend egg, oil and milk. Stir into flour mixture, blending lightly. Stir in cottage cheese and sauteed onions. Turn into buttered 9" round cake pan. Sprinkle with cheddar cheese and poppy seeds. Bake at 425~ for 25 minutes or until golden brown. Serve hot, cut in wedges.