Preheat the oven to 400°F (200°C). Roll out the puff pastry in a pie dish and prick the bottom with a fork.

Peel and thinly slice the onion. Sauté the onion and bacon pieces in a little olive oil until golden.

In a mixing bowl, whisk together the eggs, cream, salt, pepper, and nutmeg. Add the cooked onion and bacon. Mix again.

Pour the mixture into the pastry shell and sprinkle with shredded Swiss cheese. Bake for 30 minutes.