Chop up the courgettes, onion and garlic, sauté in the butter and add sugar, salt and pepper to taste.
Add the white wine and reduce, bring to the boil with the stock and cream. Continue cooking over a low flame for 20 minutes, then transfer the mixture to a blender, add the Mostarda Purée with ginger and blend.
Cut the salmon into thin strips. Pour the soup into plates and garnish with the salmon fillet strips.