Combine tomatoes, broth, tomato paste, sugar, and basil in a large pot. Simmer over medium heat 10 minutes.
Puree with an immersion blender or carefully in blender batches. Stir in cream; season with salt and pepper. Keep warm on low.
Butter one side of each bread slice. Top 4 slices, butter-side down, with 2 cheese slices each. Close with remaining bread, butter-side up.
Heat a large skillet or griddle over medium heat. Cook sandwiches 3-4 minutes per side until golden and cheese melts.
Halve diagonally; serve immediately with hot soup for dipping.