Cook the pasta in boiling salted water for about 10 minutes. In the meantime, wash salmon, dab dry and cut into coarse cubes. Halve the lemons, cut off 4 slices and squeeze the remaining lemons.
Peel and finely chop the onion. Season salmon with salt and pepper. Heat oil in a pan. Fry the salmon cubes and lemon slices all around. Remove and put aside. Sauté the onion in the frying fat and deglaze with white wine.
Pour lemon juice and vegetable stock into the wine stock. Add cream and bring to the boil. Stir in sauce thickener. Season with salt and cayenne pepper. Bring to the boil and warm the salmon in it. Wash the basil, dab dry and, except for something to garnish, pluck leaves from the stalks.
Cut the leaves into rough strips and add them to the lemon sauce. Drain the pasta, arrange in a bowl and pour the salmon with the lemon sauce over it. Garnish with the lemon slices and the remaining basil.