Place the dried porcini into a small bowl, pour over freshly boiled water and leave to soak.
Drain the sauerkraut into a sieve. If you would prefer a slightly less sour
flavour, rinse the sauerkraut with cold water and then drain it (I did this and it worked really well - just a slight tang). If you like sour, then squeeze out the liquid using your hands. Put to one side.
Heat 2 tablespoons of oil and the butter in a large ovenproof pan or Dutch oven and add the onions. Cook over a very low heat for 10 - 15 minutes, until the onions are very soft and lightly golden.
Add the pork to the pan and cook over a gentle heat for about 10 minutes, allowing it to brown slowly while the fat is released.
Add the sausages to the pan and stir. Add the sauerkraut.
Drain the porcini mushrooms (reserving the liquid), roughly chop and add to the pan. Add the allspice berries, prunes or powidta and bay leaves, and pour in the reserved mushroom soaking liquid, being careful not to add any of the grit at the bottom of the cup.
Pour in the stock and season well with salt and pepper. Cover with a lid or foil and cook in
the oven for 11/2 hours. After the first 15 minutes turn the oven down to 180C/350F/Gas Mark 4. (Alternatively, you can cook your bigos, covered, over a gentle heat on the hob).
Towards the end of the cooking time, fry the fresh mushrooms in a separate pan with the remaining oil. Add to the stew, along with the fresh cabbage, stir well, cover and place back in the oven for a further hour.
If there is a lot of liquid left in the bigos, put the pan over a medium heat and simmer, uncovered, for around 10 minutes or until some of the liquid evaporates (although I preferred mine with lots of juice!). Serve with rye bread.
The bigos is delicious eaten right away, but even better the next day after being thoroughly reheated.