Preheat an oven. Place halved tomatoes and shallots in a single layer on a large rimmed baking sheet. Drizzle with olive oil, then season with Kosher salt and black pepper.
Use a sharp knife to slice. Place each in a small square of aluminum foil, drizzle with a little olive oil. Wrap the foil tightly, place on the baking sheet along with the tomatoes.
Place in a preheated oven, then cook. Transfer the tomatoes and shallots to a blender or large soup pot. Carefully unwrap the roasted garlic, squeeze the cloves out. Add to the blender.
To the blender, add 1 cup of packed basil leaves. Stir or blend in heavy cream, then taste and adjust seasoning.
Spread butter in a thin layer on 4 pieces of bread, sprinkle with granulated garlic. When hot, place two pieces of bread butter side down on the skillet. Cook for 3 minutes, flip.
Spoon the roasted tomato soup into bowls. Sprinkle with sea salt and black pepper, top each bowl with grilled cheese croutons. Serve immediately!