For the tomato sauce, wash and finely chop the parsley. Peel and finely chop the onion. Wash tomatoes, cut into quarters and steam with onion and parsley until soft and skin curls.
Salt, pepper and strain. Prepare a preserves with butter and flour. Pour water, add strained mixture and boil well, stirring frequently.
Season the tomato sauce with salt, sugar, lemon juice and pepper.