Finely chop the sauerkraut. Peel and finely chop the onion.

In a pot, place the sauerkraut, onion, bay leaf, and allspice. Add water (adjust the amount so that it reaches a few centimeters above the contents of the pot). Bring to a boil and reduce heat. Cook on low heat for about 1 hour, stirring occasionally. Add water if needed. Meanwhile, prepare the mushrooms.

Place the mushrooms in another pot and cover with boiling water. Leave for about 20-30 minutes. Then cook the mushrooms until soft (in the same water), about 10-15 minutes.

Drain the mushrooms and finely chop them. Add to the sauerkraut towards the end of cooking. Mix well. Season to taste with salt and pepper. Mix.

Serve hot or cold. Store in the refrigerator for 5-7 days.