Sweet Potato Puffs

1/4 cup butter, melted

1 tablespoon lemon juice

1 teaspoon salt

1/8 teaspoon pepper

2 cups hot mashed potatoes

1/4 cup nonfat dry milk

1/2 cup water

2 eggs, separated

Blend melted butter, lemon juice, salt and pepper into hot mashed sweet potatoes. Gradually beat in nonfat dry milk and then hot water; continue beating until smooth and fluffy. Beat egg yolks until thick and light yellow. Fold into sweet potato mixture. Pour into greased 1-quart casserole dish. Bake in moderately hot oven (400 F) until firm and golden brown, about 35 minutes.