Onions peel, quarter and in thin slices cut. Fry in hot oil. Season with salt and pepper. Sprinkle with paprika and sauté briefly. Stir in a good 1/2 l water, sherry and stock, bring to the boil. Simmer covered for about 20 minutes.
Wash and chop the parsley and add to the soup. Grate cheese finely. Toast slices of bread if necessary. Season soup to taste and pour into ovenproof soup bowls. Put bread in, sprinkle cheese on top. Bake in a preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/gas: level 4) until golden brown