Halve the onion without peeling. Peel and dice one half. Crush the pepper and allspice grains. Wash thyme. Beat egg whites until stiff. Roast the onion half with the cut surface facing down in a large saucepan without fat. Add all soup ingredients except sherry and fresh tomatoes. Bring to the boil, stirring occasionally. Simmer on low heat for an hour over a mild heat.
Line a fine sieve with a cheesecloth (kitchen paper can also be used, not chlorine-bleached), pour the soup through. Important: do not stir or squeeze in the sieve, otherwise the soup will be cloudy. Heat the soup and season with sherry, salt and pepper.
For the patties, mix egg yolks, flour, a little salt, parmesan and milk into the pancake batter. Bake thin pancakes in a little fat, roll up.
Just before the guests arrive: heat the soup, cut the pancake rolls into thin slices. Scald the tomatoes with boiling water, peel and core them and cut the flesh into wedges. Divide the tomato wedges and patties on six plates, add the heated soup and serve.