Peel and chop the onion and fry in the butter in a wide pan until translucent. Pour in the cream and simmer for 3 minutes. Dice the ham and add to the sauce. Peas as well. Season to taste with sugar, salt and pepper.
Let the sauce steep and cook the pasta.
When the pasta is done, stir the parmesan into the sauce and immediately fold in the drained pasta. If the cheese is too early in the sauce, it will be too firm.