Heat oil in a saucepan over medium heat. Add the onions and sweat a bit.
Add the garlic, thyme, bay, tomato paste, and tomatoes. Season mixture with the sugar, salt and pepper. Add the stock and bring to a boil. Reduce heat, cover, and cook for 15 minutes. Stir occasionally.
Remove bay leaf and discard. Puree mixture in a blender and strain back into the saucepan.
Just before serving, reheat and incorporate cream. Check the seasoning.
Divide among serving bowls and garnish with chervil leaves (or green onion slivers).