From the salmon fillets, cut 8 pieces, about 2 inches thick.
Take each piece, skin down, and slice right through the middle, carefully not to cut through the skin. This way, each steak opens in butterfly shape. Put salt and pepper on each steak.
Set oven at 425F.
Fry the onion lightly in 2 tablespoons of butter, until translucent.
Add the tomato paste, and let it cook with the onion for just a half a minute.
Add the wine, and crumble in the fish cubes.
Bring to a boil, reduce the heat, and let it cook until it reduces to about half.
Add the creme fraiche and cook while whisking with a hand beater. Add salt and white pepper to taste.
Whisk in 2 tablespoons of butter and sift the sauce which is now ready.
Up to here, you can prepare 3 – 4 hours before serving.