Cook the Vegetables: Heat a pan over medium heat and cook the minced onion, minced garlic, and spinach for 2–3 minutes.
Prepare the Egg Mixture: In a bowl, combine the eggs, flour or cornstarch, cream, grated cheese, salt, and pepper. Whisk until the ingredients are well combined.
Add the Filling Ingredients: Add the cooked onion, garlic, and spinach mixture to the egg mixture, followed by the diced fresh salmon. Stir until everything is evenly combined.
Prepare the Pastry: Place the puff pastry into the mold, pressing it into the base and sides as needed. Prick the bottom of the pastry several times with a fork.
Fill the Pastry: Pour the prepared egg, salmon, and spinach mixture evenly into the pastry-lined mold.
Bake the Quiche: Bake at 190°C / 375°F for 40 minutes, or until the top is golden brown and the filling is set in the center.
Check for Doneness: The quiche is ready when the surface has developed a golden-brown color and the center of the filling has set.