2 lg. onions, sliced
1 qt. milk
1/2 tsp. nutmeg
1 tbsp. butter
1 tsp. salt
1 egg yolk

Bring onions, milk, nutmeg, butter and salt to a slow boil and cook until onions are tender. Beat egg yolk in a small bowl and add a little of the hot soup, beating it. Pour the mixture back into the soup and cook a few minutes longer.