Soak the dried mushrooms in 250ml/1 cup boiling water and set aside.
In a large and deep pan cook bacon in olive oil, remove from the pan with a slotted spoon and set aside.
To the same pan add onions and cook on medium heat for 5-7 minutes until slightly coloured, add garlic and mushrooms with a tablespoon of butter, saute until the mushrooms are soft. Add the stock and scrape the bottom of the pan with a wooden or plastic spatula to release the brown bits into the stock.
Add sliced cabbage, drained and chopped dried mushrooms, bacon, tomato paste and bay leaf, stir to combine, lower the heat and cover with a lid. (If the cabbage doesn't fit in the pan, add 2/3 of the amount and cover with a lid for 10 minutes, then add the rest when the volume of the cabbage in the pan goes down.)
Braise the cabbage for 1 hour-1 hour 15 minutes with a lid on while stirring once in a while to prevent the bottom from burning.
At the end of the cooking time the volume of the cabbage reduces by roughly a half and the colour turns from bright green to golden brown. There should be no liquid left in the pan. Stir in sour cream and warm through for 1 minute.
Season with salt and pepper last as it's easy to oversalt in the beginning stage when the volume of cabbage is significantly higher.