Brush 12 fluted paper bun cases with the melted butter or oil, and place on a baking sheet. Make a thick, smooth white sauce with the butter, flour and milk, and cook for 5–10 minutes. Remove from the heat, add the cheese, and stir until melted. Beat in the egg yolk. Whisk the whites until firm, and fold into the egg and cheese mixture. Spoon into paper cases to within