Peel and wash the potatoes, cut in half lengthwise and cook in salted water for about 20 minutes. Peel and wash carrots and cut them diagonally into slices. Steam in 1⁄4 l boiling water with the broth for about 5 minutes.
Drain and collect the cooking water.
Heat 2 tablespoons of butter. Sauté the flour in it. Stir in cooking water and milk, bring to the boil. Let simmer for about 5 minutes. Season to taste with salt, pepper and nutmeg.
Wash and chop the chervil, except for something to garnish. Clean and wash spring onions and cut into rings. Layer the carrots in a greased casserole dish. Sprinkle with chervil. Drain the potatoes and lay them on the carrots with the smooth side down.
Add spring onions. Pour sauce over it. Grate cheese and sprinkle over potatoes.
Bake in a hot oven (electric range: 200 °C/circulating air: 175 °C/gas: level 3) for approx. 15 minutes until golden brown. Garnish with chervil.