Put sour cream in a measuring cup. Add sour milk or buttermilk to fill cup. Pour into a large bowl and add the egg, salt and melted margarine. Blend well. Gradually, by hand, add flour and baking soda, until everything is mixed and blended. Remove to a mixing board and knead until smooth. Let stand 3 hours or leave in refrigerator overnight. Divide dough into serving pieces. Roll each piece 1/4- inch thick; cut 2 parallel slits in the center to make ears. Fry in hot oil until golden brown. Dip each piece in cinnamon and sugar.