Prepare the ingredients before starting: mince the onions, open the tomatoes, slice and chop the basil.
If possible, use what is called a non-reactive pot for this recipe. Stainless steel or enamel coated metal are an example of that. Aluminum pans are reactive and don't mix well with tomatoes.
Melt the butter in your soup pan.
Add the onions and cook until soft, about 4 minutes.
Add the tomatoes with the liquid.
Add the chicken broth.
Stir in the sugar.
Let all of these ingredients cook at a low boil for about ten minutes.
Add the heavy cream and continue cooking about 4 minutes.
Blend your soup. I used an immersion blender and kept some chunky tomatoes. You can also use a regular blender, but be VERY CAREFUL not to overfill it. You can easily burn yourself with the hot liquid.
Once the soup is your desired consistency, stir in the Parmesan until it melts.
Add the basil and stir.
Season with salt to taste. My tomatoes had sea salt, so I didn't need to add more than a quick grating over the surface.
Return your soup to the stove and heat through, about 3-4 minutes.