01 -
In a large bowl, mix the flour, salt, and butter, rubbing the mixture with your fingers until it resembles fine breadcrumbs.
02 -
Add the egg and cold water. Knead the dough until smooth.
03 -
Shape the dough into a ball, wrap it in cling film, and chill in the refrigerator for 30 minutes.
04 -
Thinly slice the onions into half-rings.
05 -
Melt the butter over medium heat and sauté the onions until soft and caramelized (about 20 minutes). Stir frequently to avoid burning.
06 -
In a bowl, whisk together the eggs and cream. Add grated cheese, salt, pepper, and nutmeg. Mix well.
07 -
Roll out the chilled dough and line a tart pan (about 23 cm in diameter), forming the edges. Prick the base with a fork.
08 -
Spread the caramelized onions over the crust and pour the cheese and cream mixture on top.
09 -
Bake at 180°C (350°F) for 25-30 minutes, until the filling is golden and set.
10 -
Let the tart cool slightly before slicing. It tastes great both warm and cold.