Separate the chard leaves from the stems. Cut stems into small pieces, cut leaves into strips, wash separately. Cut the onion and garlic into small cubes. Heat the olive oil in a high pan, sauté the onion and garlic cubes until translucent, then add the stalks and sauté briefly. Pour in the vegetable stock and simmer covered for approx. 5 minutes.
In the meantime, cook the pasta.
Then add the strips of leaves to the sauce, simmer until they collapse, stirring frequently. Stir in the tuna with the whipped cream and the crème fraiche, season with Parmesan, salt and pepper and continue to cook covered on a low heat, stirring again and again.
Before serving, add a squeeze of lemon to the sauce, chop the basil and add. Then stir again vigorously and serve with the pasta.