Rinse the salmon, pat dry and place in a buttered baking dish.
Peel and finely dice the onion. Sprinkle in the mold. Mix the grated parmesan with the cream, tomatoes, mustard, lemon juice and white wine, season with salt, pepper, thyme and, if desired, with chilli flakes and green pepper. Pour the sauce over the salmon, sprinkle with cheese if you like (works fine without it) and bake for 25 minutes.
Pasta and green salad go well with this. Also good with white bread as the sauce is plentiful.
Of course, you can sauté the onions beforehand and cook a sauce, we like it that way too.