In a medium saucepan, combine the plum tomatoes with the water, tomato paste, onion, garlic, oregano, crushed red pepper and granulated sugar. Simmer over moderate heat, stirring a few times, until the tomatoes are very tender, about 20 minutes. Add the cream and simmer for 1 minute.
Puree the soup in a blender and pass it through a coarse strainer into a medium bowl. Season with salt and black pepper. Refrigerate the soup until cold, about 1 hour.
Meanwhile, preheat the oven to 375°. Spread the cherry tomatoes on a rimmed baking sheet and toss with the olive oil, confectioners' sugar and a large pinch of salt. Bake for about 10 minutes, until the skins start to wrinkle. Transfer the tomatoes to a bowl and toss with the dill.
Ladle the soup into bowls, garnish with the roasted cherry tomatoes and serve.