Peel and chop the onions. Celery peel, wash and cut into large cubes. Dab ox cheeks dry, season with salt and pepper. Heat the oil in a frying pan. Fry the meat in it for about 5 minutes. Take out. Fry the onions and half of the celery in hot frying fat for about 2 minutes. Add tomato paste and sweat briefly. Deglaze with port wine and about 500 ml water. Bring to the boil, add ox cheeks and braise covered in the preheated oven (electric cooker: 160 °C/circulating air: 140 °C/gas: see manufacturer) for about 4 hours.
Peel, wash and cut the potatoes into large pieces. Boil potatoes and the rest of the celery in salted water for about 20 minutes. Peel, wash and slice carrots.
Drain the potatoes and celery. Add 3 tablespoons of butter and milk. Mash everything to fine puree. Season to taste with salt and nutmeg. Heat 1 tablespoon butter in a frying pan. Sauté carrots in it. Sprinkle with sugar and let it caramelize slightly. Season with salt and pepper. Add almost 100 ml water, bring to the boil, cover and simmer for about 8 minutes.
Lift the ox cheeks out of the sauce. Bring the sauce to the boil and reduce for about 5 minutes. Season to taste with salt and pepper. Cut open the cheeks and arrange everything.