Preheat the oven to 400°F.
Grease a pie dish with butter.
Place the puff pastry in the dish and trim the edges to fit.
Prick holes in the dough with a fork.
Finely chop the leeks and sauté in olive oil over medium heat until softened.
Pour the sautéed leeks into the prepared dish.
Add the sea asparagus and salmon pieces, seasoning with pepper and salt.
In a bowl, whisk together the eggs, heavy cream, crème fraîche, pepper, and salt until smooth.
Pour the egg mixture over the salmon and leeks.
Sprinkle grated cheese evenly over the top.
Fold in the edges of the puff pastry to form a border.
Bake in the preheated oven for 30 minutes, or until set and golden brown.
Check doneness by pricking with a fork; if it comes out clean, the quiche is ready.