Preheat oven to 350 F.
Pre-bake the piecrust for 10 minutes.
Add the sautéed onions to the piecrust. In a medium bowl, combine the eggs, cream and grated Jarlsberg. Season with lavender and chiles.
Place half the sardines and half the tomatoes on top of the onions. Add the cheese-and egg batter and spread it out evenly with a rubber spatula. Place the remaining sardines and tomatoes on top in a circular form.
Bake the quiche in the middle of the oven for 35 to 45 minutes, until almost firm. Let stand 10 minutes before serving.