01 -
Preheat the oven to 180°C (350°F).
02 -
Peel and slice the onions thinly.
03 -
In a large skillet, melt the butter and add the onions. Cook over low heat until golden and caramelized, about 20-25 minutes.
04 -
In a bowl, whisk the eggs with the heavy cream. Add the grated cheese, salt, pepper, and nutmeg if desired.
05 -
Roll out the pastry dough in a tart pan and prick the base with a fork.
06 -
Place the caramelized onions on the dough and pour the egg and cream mixture over the top.
07 -
Bake for 35-40 minutes or until the tart is golden and set.
08 -
Allow to cool slightly before serving.