First heat 1-2 tablespoon butter. Immediately steam the finely chopped shallot until translucent. In the meantime, whip 1 cup of cream with the mixer and heat it with the onion. Add 2 tablespoons of ketchup to the cream, possibly more, until the sauce turns a nice pink color. Finally add the cognac to the sauce and bring to the boil. Season to taste with a little pepper and a soup cube. In addition, add 2-3 cloves of garlic, finely pressed, to the boil. Now let the sauce simmer for 15 minutes or whip it up briefly with the hand blender and extend it a little with cream if necessary. Finally, add the sauce with cold butter. Add the salmon, but don`t let it cook too long as it will disintegrate too much.
Meanwhile, cook the tagliatelle in salted water until al dente. Mix the pasta and salmon sauce just before serving. A simple green salad goes very well with it.