Combine flour, salt, dry mustard, sugar, cayenne pepper and 3 tablespoons Brown's Buttermilk in the top of a double boiler. Beat egg well; stir in remaining Brown's Buttermilk and orange juice. Stir into flour mixture slowly. Cook, stirring constantly, until thickened. Remove from heat; stir in lemon juice and chill. Serve on vegetables, mixed greens or fruit salads.