For the onion tart, first prepare the dough. To do this, mix flour with butter, curd, yolks and a pinch of salt and quickly knead into a smooth dough. Wrap in cling film and leave to rest in a cold place for 4 hours.
Cut onions in half and slice. Heat olive oil in a frying pan. Sauté onions (without young onions) in it, stirring constantly, remove from heat and let cool.
Preheat oven to 200 °C, butter cake pan. Roll out dough on a floured work surface to the thickness of the back of a knife and line the pan with it so that the dough is about 2 cm above the edge. Spread onions evenly on top.
For the glaze, whisk the eggs with the cream. Cut leek and onions – only the white part – into rings and stir in together with chopped bacon and grated cheese. Season the mixture with salt, pepper and nutmeg and pour over the onions. Form the edge of the dough into an attractive bead between your thumb and forefinger.
Bake the onion tart in the oven for about 40 minutes. Remove and let rest for 10 minutes before cutting.