Preheat the oven to 450°F.
Cut the tomatoes in chunks (or in half, widthwise, if you're using Roma tomatoes) and place them on a large rimmed baking sheet or in a roasting pan with the cloves of garlic. Drizzle them with olive oil and sprinkle with salt and pepper. Roast for about an hour, until the tomatoes are juicy with dark edges and the garlic is very soft. Set it aside to cool for a bit.
If you have a hand-held immersion blender (I highly recommend one), transfer the tomatoes, garlic and all the juices that have collected in the pan into a medium saucepan and set it over medium heat. If not, transfer it to a blender or food processor, puree it (add a little stock if you need to get it moving) and then transfer it to a pot. Add the chicken stock and sugar. Bring to a simmer and cook for about 10 minutes. If you are going to add cream, turn the heat down to low and add it at the last minute, stirring just until the soup is heated through.
If you like, stir in a small handful of chopped fresh basil or a spoonful of pesto just before serving.