Wash the potatoes and cook in boiling water for about 20 minutes. Blanch sugar snap peas in boiling salted water for about 3 minutes and rinse in cold water. Melt margarine, dust with flour and sweat for about 3 minutes.
Slowly stir in stock and "cooking with finesse". Bring the sauce to the boil and season to taste with salt, pepper and nutmeg. Simmer for 1 minute. Wash the cherry tomatoes and pat dry. Drain potatoes, rinse and peel.
Place the potatoes in a greased casserole dish. Halve the ham. Spread cherry tomatoes, snow peas and ham between the potatoes. Pour béchamel over the vegetables. Bake in a preheated oven (electric cooker: 250 °C/ convection oven: 225 °C/ gas: level 5) until golden brown.
Wash the chervil, dab dry and garnish the potatoes with it.