Cook the cauliflower cut into florets in salted water and then drain in a colander.
Make a roux with the margarine and flour, deglaze with milk and yoghurt and simmer for a few minutes. Add the parmesan, salt and a pinch of nutmeg and stir in the egg yolks.
Place the cauliflower florets in a greased baking dish and pour the yogurt sauce over them. Sprinkle the breadcrumbs on top and distribute the butter in flakes on the casserole.
Cook in a preheated oven at 200 ° C top / bottom heat for about 50 minutes.