Sieve the flour on a work surface, crumble the butter into it, season with a pinch of salt and knead everything into a smooth dough by gradually working in the water. Let the dough rest for 30 minutes.
Then press into a greased fruit cake tin, springform tin or quiche tin, prick several times with a fork and prebake in a preheated oven at 180 degrees for approx. 5 minutes.
Blanch the ham strips in boiling water for 2-3 minutes, remove them, mix with the onion rings and spread on the dough base. Beat the eggs, whisk with crème fraîche, season with salt, pepper and nutmeg and pour the mixture onto the cake. Bake in the preheated oven at 180 degrees for about 30 minutes.