First preheat oven to 175°. Chop the bacon into small pieces, add to a heated frying pan and cook until almost crispy. In the meantime slice the leeks finely and wash until all soil is gone, drain, add to pan. Saute gently. Slice the onion very finely add to the leeks and soften down.
Add the cream and all the seasonings. Heat through for a few minutes. Take off heat, cool down. Put into an ovenproof dish, then add the grated cheese.
Cook until cheese has become golden brown. Serve hot. You can just cook so that cheese is melted. Cool down, put in fridge. Next day cook in oven until cheese has browned.
