Knead the dough ingredients into a smooth dough and refrigerate for an hour.
Grease a 26 cm diameter tart, flan or springform pan and sprinkle with breadcrumbs, press the dough into a plate and pull up one edge. Prick the base several times with a fork and prebake in a preheated oven at 200 ° C for 10 minutes.
Coarsely grate the cheese. Finely chop the peeled onions, sauté them briefly in butter and then let them cool down a little. Mix the cheese with the onions and spread on the pre-baked base. Mix the eggs, crème fraîche, cream, spices and cornstarch together, then add the finely weighed parsley. Pour the egg mixture over the cheese and onion mixture and bake the flan at 175 ° C for 40 to 45 minutes.