Wash the potatoes and cook in boiling water for about 20 minutes. Drain, rinse with cold water, peel and halve. Clean broccoli and cauliflower, wash and cut into small florets. Cook the cauliflower in 1/2 litre boiling salted water for about 10 minutes.
Add broccoli after about 3 minutes and cook. Drain the vegetables and collect the cooking water. For the sauce, peel and finely chop the onion. Grate cheese. Melt the fat. Sauté onion in it.
Dust with flour and allow to sweat. Deglaze with 400 ml vegetable water and cream. Bring to the boil while stirring and simmer for about 5 minutes at low heat. Melt half the cheese in it. Season to taste with salt, pepper and nutmeg.
Roughly chop the almonds. Divide the vegetables and sauce into 4 ovenproof dishes. Sprinkle with remaining cheese and almonds. Bake in the preheated oven (electric: 200 °C/ gas: level 3) for about 5 minutes.