Mix flour, salt, 125 g fat, 1 egg and 1 tablespoon of ice water to a smooth dough and cover and chill for about 30 minutes. In the meantime, peel and halve the onions and cut them into thin slices.
Heat the remaining fat in a pot. Fry the onions in it until transparent. Season with salt and pepper, take out and let cool down. Whisk remaining eggs, milk and cream. Season with salt, pepper and nutmeg.
Roll out the dough to a circle (approx. 28 cm Ø). Place in a tart tin (26 cm Ø) and press the rim firmly down. Put onions on the dough and pour the egg milk over it. Bake in a preheated oven (electric: 200 °C/ gas: level 3) for about 40 minutes.
Results in about 8 pieces.