Clean and wash the spring onions and cut into fine rings. Heat the butter in a saucepan and sauté the spring onion rings in it. Dust with flour and sauté briefly while stirring. Pour in the stock while stirring, bring to the boil and simmer for about 3 minutes.
In the meantime, cook the pasta according to the instructions on the packet. Cut salmon into strips. Add frozen peas to the sauce and simmer for about 3 minutes. First stir the cream cheese into the sauce, then add the salmon and tarragon (amount to taste) and heat briefly. Season to taste with pepper. Since salmon is usually already spicy / salty enough, only add salt carefully as required. Serve the pasta with the sauce.