Halve the mushrooms, cut the onions into strips. Cut the sausage into slices. Peel and dice the celery. Clean the leek and cut into strips. Peel and dice the potatoes. Cut the meat into strips.
Heat the oil in a casserole. Fry the meat in portions for approx. 5 minutes. Season with salt and pepper and remove. Fry the onions and mushrooms in the hot frying fat for approx. 4 minutes. Add the potatoes, celery and leek and fry briefly. Deglaze with a good 3/4 l water and ketchup. Add the meat and sausage, bring to the boil and stew covered for approx. 45 minutes.