Defrost the puff pastry. Peel and halve the onions and cut them into thin strips. Dice bacon finely.
Fry bacon in 2 tablespoons of hot fat until crispy. Add onions and fry for about 10 minutes until transparent. Season with pepper and a little salt, let cool down.
Grease 4 small quiche moulds (each approx. 15 cm Ø) or one large one (approx. 30 cm Ø). Roll out the dough slices slightly larger (approx. 19 x 19 cm) on a little flour. Line the moulds, press the edges and cut off any protruding corners.
Sprinkle the bottom with breadcrumbs.
Whisk milk, cream and eggs. Season with salt, pepper and nutmeg. Spread the onion-bacon mixture in the moulds and pour the egg milk over them. Bake in the preheated oven (electric cooker: 200°C/circulating air: 175°C/gas: level 3) on the lowest rack (gas: see cooker manufacturer) for approx. 30 minutes.
Serve hot. Drink: cool beer or white wine, e.g. Riesling.