Bigos is not bigos without mushrooms – dried porcini and/or morels add a special flavour. Some people use fresh cabbage and sauerkraut. My preference is for all sauerkraut, no fresh cabbage or at least two parts sauerkraut to one part fresh cabbage).
Here is a bigos "proto-recipe". Keep in mind that this is a basic, no-frills bigos. It works better if you add your own ingredients (including about a half cup of ketchup – I am not kidding). Traditionally, you use the same weight of cabbage as you do meat. I think it works better with more sauerkraut/cabbage than meat.
-2 kg fermented cabbage (sauerkraut)
-500 g pork or venison or beef
-250 g sausage
-250 g bacon
-a handful of dried mushrooms
-fresh mushrooms if you like
-a medium onion, chopped
-whole black peppercorns, salt, bay leaf or two, tsp or two of carraway seeds
-a tomato or two, some ketchup, leftover spaghetti sauce (they all work)
-a bit of flour for dredging the meat
(You can add a chopped apple, chopped celery, fresh cabbage, more onion etc. Whatever you like. Don’t add carrots – they "sour" the mixture.)
Cut up the bacon and fry it with the onions.
Remove and leave the fat.
Chop up the meat and dredge it in the flour.
Brown it in the leftover fat.
Put this in a large pot with the sauerkraut, bay leaf, peppercorns, carraway seeds
Soak the mushrooms in about a cup of boiling water to soften.
Add them to the pot.
Now you cook this for at least three hours, adding seasonings or ingredients to taste as you go along. It improves upon reheating and is ideally made a day or two before you plan to serve it.
As Lenusz said, every cook has her/his own recipe for bigos. All amounts are approximate.