Heat 1 tablespoon butter in a large saucepan. Steam the onion in it until translucent. Add the risotto rice and sauté as well. Gradually add the hot broth to the rice until it has absorbed the liquid well.
In the meantime, heat a pan and fry the prawns and salmon well in the remaining butter. Drain on paper towels.
After about 20 minutes, the rice should have absorbed the liquid. Add the prawns and salmon. Add the cream and mix in the parmesan. Simmer for about 5 minutes until the cream is well absorbed by the rice. Season with salt and pepper and serve.