Bring the soup to a boil. Pour in the meat and simmer on a low fire with the lid closed until tender, 2 1/2 to 3 hours before boiling point.
Remove the boiled meat from the pan. Boil the soup on a large fire to 8 dl (if preparing originally 15 dl of soup).
Finely slice the pickles.
Coarsely chop the onions and sauté them in the butter-oil mixture until light yellow. Sprinkle the flour on top and sauté everything together for another three to four minutes, turning.
Add the vinegar, tomato puree, pickles and boiled soup. Season with salt and pepper. Cook on low fire for twenty minutes.
Cut the boiled meat into slices as narrow as possible. Grease a baking dish with butter. Spread one third of the onion sauce evenly in it. Layer the meat like a brick and form the remaining sauce over it.
Cut the toast into small cubes and sprinkle over the gratin. Meanwhile, bake in the oven heated to 220 degrees on the second rack from the bottom for about twenty-five minutes.
Tip:
Boiled meat can be cooked the day before. Keep in the soup.
A few hours before eating: Cook the onion sauce and finish the boiled meat gratin until ready to bake.
Our tip: Use your favorite red wine for cooking!