Clean, wash and thinly slice the vegetables. Wash the herbs, dab dry, put something aside for garnishing. Finely chop remaining herbs. For the sauce, heat fat, sweat flour in it and deglaze with broth and milk.
Bring to the boil briefly and stir in the cheese. Mix the egg yolk and crème fraiche. Remove the sauce from the heat, stir in the crème fraîche and season with salt and pepper. Stir the herbs into the sauce, except for one tablespoon.
Layer some sauce, lasagne dishes and vegetables in a greased casserole dish. Finish with lasagne platters and sauce. Sprinkle with sunflower seeds. Bake in a preheated oven (electric: 200 °C/ gas: level 3) for about 45 minutes.
Sprinkle with remaining herbs and garnish before serving.