Wash the potatoes and cook in boiling water for about 20 minutes. Drain, rinse with cold water and peel. Cook peas in boiling salted water for 3 minutes. Pour off, rinse with cold water and drain.
Cut the potatoes into slices. Separate 2 eggs. Mix quark, 50 g cheese, 1 egg, 2 egg yolks and 100 ml milk. Season with salt and pepper. Beat egg white and 1 pinch of salt until stiff. Fold into the quark mixture.
Grease the casserole dish well. Alternately layer potatoes, peas, quark mixture and ham slices in the casserole dish. Sprinkle with 50 g cheese. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 40-45 minutes.
For the chive sauce melt the fat in a pot. Dust with flour and sweat while stirring. Add 350 ml water and 150 ml milk while stirring. Bring to the boil, stir in stock and simmer for 10 minutes.
Stir now and then. Wash the chives, dab dry and cut into fine rolls. Stir into the sauce. Garnish casserole with chervil. Add the chive sauce.