In a large heavy pot, heat the olive oil over medium heat. Add the onions, sugar, and salt. Cook for 8 to 10 minutes, or until the onions are translucent and soft.
Stir in the diced tomatoes with the liquid and the chicken broth. Bring the soup to a boil; then turn the heat to low and simmer gently for 15 minutes.
Pour in the cream, and using an immersion blender, puree the soup until smooth. (If you do not have an immersion blender, carefully pour the soup into a blender, filling it no more than three-quarters full, and venting the lid to allow the steam to escape. Be careful not to fill the blender to the top or tomato soup will explode all over your kitchen! Puree until smooth. Return the soup to the pot and reheat if necessary.)