Roughly dice the onion. Drain the pineapple while collecting the juice. Cut the pineapple rings into pieces. Clean and wash the leek and cut into rings. Pat the meat dry with a piece of kitchen paper. Possibly cut into smaller pieces.
Put the meat, onions, leek, tomato paste and pineapple in a roaster. Add the tomatoes, 100 ml pineapple juice and stock. Season with salt, pepper and paprika powder and mix everything together. Cover the roaster in the preheated oven (top / bottom heat: 175 ° C / convection: 150 ° C / gas stove: level 2) and cook the soup for about 3 hours.
Season the soup again with salt, pepper and vinegar. Parsley and marjoram leaves, except for something to garnish, pluck and finely chop. Serve sprinkled with herbs and garnished. You can also prepare the soup in a Roman pot.