Put 250 g all-purpose flour, 120 g low-fat quark, 120 g butter, 1 egg and 0.5 tsp salt in a bowl and quickly work them into a dough with a dough hook or by hand.
Wrap the dough in plastic wrap and put it in the fridge for at least 1 hour.
Clean the 2 stalks leek and cut them into thin rings.
Halve the 4 onions and cut them into strips.
Stack the 125 g bacon on top of each other and cut into small pieces.
Heat 2 tbsp clarified butter in a pan and fry the bacon until golden brown.
Add the sliced leek and onions and sweat for approx. 10 min until translucent.
Season with approx. 0.25 tsp salt and pepper and let cool.
Coarsely grate the 100 g Appenzeller or Emmental.
Preheat the oven to 200 °C (400 °F), conventional oven (top and bottom heat).
Whisk 150 ml heavy cream and 3 eggs with 0.5 tsp salt, pepper and nutmeg and season generously.
Butter a tart pan (approx. 28 cm diameter) and dust it with flour.
Take the dough out of the fridge and roll it out so that it is a little larger than the tart pan.
Place the rolled-out dough in the pan and trim off the overhanging edge.
Spread the leek and onions over the crust, pour the egg and cream mixture over them and sprinkle with the grated cheese.
First bake the leek quiche on the middle rack for 20 min. Then turn the oven down to 175 °C (350 °F) and bake for another 10-15 min.
Let the leek quiche cool a little before serving.
A green salad with seeds goes perfectly with it.