Clean the cabbage, place in plenty of boiling water and remove 12 leaves. Use the rest of the cabbage for other purposes. Peel 1 onion and chop finely. Knead the mince, egg and onion. Season with pepper.
Cut the cucumbers in half. Place 2 cabbage leaves on top of each other. Place 1 bacon slice on each. Spread the ground pork on top. Cover each with 1/2 cucumber and roll up. Wrap up with kitchen string. Heat 2 tablespoons of oil in a roaster.
Brown the cabbage rolls all around. Add stock, bring to the boil, cover and cook for about 40 minutes. Peel and wash potatoes and cook in boiling salted water for about 25 minutes. Drain potatoes. Add milk and butter.
Mash the potatoes. Season with salt, pepper and nutmeg. Peel remaining onion and cut into rings. Heat 1 tablespoon of oil in a pan. Fry the onion rings until golden brown. Take out the cabbage rolls.
Boil up the sauce, thicken with sauce thickener. Season to taste with salt and pepper. Arrange cabbage rolls, sauce and puree on plates. Add onion rings and garnish with parsley.