Peel, wash and cut the potatoes into pieces. Cover with cold water. Wash the Brussels sprouts, drain well and clean them. Pluck about 2 leaves from each cabbage and put them aside.
Cut the florets in half. Cook the potatoes and halved florets in little boiling salted water for about 15 minutes. Wash and quarter the tomatoes and remove the seeds. Finely dice the flesh. Wash parsley, dab dry and chop, except for a little bit for garnishing.
Heat the oil in a pan and fry the sausages for 5-6 minutes, turning. Warm up the milk. Drain the potatoes, add warm milk and butter and mash. Season with salt, pepper and nutmeg and stir in parsley.
Put the brussels sprouts leaves in boiling salted water for about 1 minute, pour onto a sieve and drain. Cut the bratwurst diagonally into slices and arrange on plates with the mashed brussels sprouts and potatoes.
Sprinkle with diced tomatoes and brussels sprouts. Serve garnished with parsley.