Wash the potatoes and cook in boiling water for 15-20 minutes. Clean and wash broccoli and cut into florets. Cook in 1 liter of boiling salted water for 6-8 minutes. Drain the broccoli and collect the cooking water.
Drain the potatoes as well, rinse with cold water and peel. Leave to cool a little. Peel onion and chop finely. Heat the fat in a saucepan. Fry the diced onion until transparent. Add flour and sauté while stirring.
Add cream and 1/2 l vegetable water bit by bit and bring to the boil. Add half of the cheese and let it melt. Season sauce with salt and pepper. Cut the potatoes in half if necessary and put them in a shallow casserole dish with the broccoli.
Add 2/3 of the sauce and mix well. Place slices of meat on top. Pour the rest of the sauce over it. Sprinkle with remaining cheese. Bake in a preheated oven (electric: 200 °C/ gas: level 3) for 20-25 minutes.
Wash parsley, dab dry and chop. Sprinkle over the casserole.