Finely dice the peeled onions. Cut the ham into narrow strips.
Melt the fat in a large saucepan and sauté the onion until translucent. Add the peas, sugar and broth and cook over medium heat for 20 minutes. Mix the cream with the cornstarch and add to the soup. Bring to the boil briefly and season with lemon juice, salt and white pepper. Garnish with parsley.