Clean, wash and slice the celery. Peel, wash and cut carrots into pieces. Peel, wash and halve or quarter potatoes. Cut sausage into thin slices. Peel and chop garlic.
Preheat the oven (electric cooker: 200°C/circulating air:175°C/gas: level 3). Mix vegetables, potatoes, sausage, rosemary and oil. Spread on a fat pan or a flat roasting pan. Season with salt and pepper.
Roast in a hot oven for about 20 minutes. Turn from time to time.
Dissolve the stock in a good 1⁄8 l of hot water, pour over the vegetables and continue to braise everything for about 25 minutes. Crumble the feta cheese and sprinkle over the vegetables about 15 minutes before the end of cooking. Season to taste with salt and pepper.