Soak toast in cold water. Clean and wash the broccoli, cut the floret from the stalk. Peel and chop the stalk. Peel potatoes, wash thoroughly. Peel onions and finely dice 1 onion.
Knead the minced meat, diced onion, crushed bread, mustard, 1 1/2 tsp. salt, pepper and egg. Form 8 meatballs from it. Cook potatoes in boiling salted water for about 25 minutes. 12 minutes before the end of the cooking time add the broccoli and cook.
In the meantime cut 4 onions into slices. Caramelise the sugar in a pan until golden. Deglaze with 175 ml boiling water and vinegar. Simmer without lid for about 8 minutes at low heat.
Add onion slices and let it simmer for another 8-10 minutes. In the meantime heat oil in a pan and fry the meatballs on each side for about 4 minutes at medium heat. Heat milk and butter in a saucepan.
Drain the potatoes and broccoli, add the milk-fat mixture, mash roughly and season with nutmeg. Arrange broccoli-potato puree, meatballs and balsamic onions on plates.