Drain canned tomatoes, remove stalks and seeds. Collect the juice.
Steam with balsamic vinegar, salt, olive oil, pepper and a touch of sugar for 10 min at lowest temperature. Next add 3-4 tbsp of juice.
Clean the herrings, cut the heads into small pieces, dab them, then season with salt and turn them in flour on the other side. Fry in a mixture of sunflower oil or other vegetable oil and butter until golden brown.
Peel the onions, quarter them and divide them into slivers – sprinkle with a little sugar and sauté in butter until soft – this will give a nice color.
Extinguish with a little water and sauté for a good 10 minutes until soft. Mix the onions and the tomatoes and bring to the table with the fried herrings.
Lightly acidify the herrings with lemon and sprinkle with parsley.