Preheat Oven: Set your oven to 400°F and line a baking sheet with parchment paper.

Roast Vegetables: Place tomatoes (cut side up), onion wedges, and garlic cloves on the sheet. Drizzle with olive oil and sprinkle with salt, pepper, and sugar. Roast for 45 minutes or until vegetables are very tender. Allow to cool slightly, then peel the tomatoes and remove any stems.

Make Grilled Cheese: While vegetables roast, butter one side of each bread slice. In a skillet over low heat, place one slice buttered side down, add cheddar, and top with another slice buttered side up. Cook until golden and cheese is melted (about 3 minutes per side). Repeat with the remaining bread and cheese. Cut each sandwich into small cubes.

Blend the Soup: Add roasted vegetables to a large pot. Pour in chicken broth and chopped basil. Use an immersion blender to blend until smooth.

Heat and Finish Soup: Warm the blended soup over medium heat. Stir in heavy cream, Parmesan, and garlic salt. Cook until cheese is melted and soup is heated through.

Broil the Bowls: Move oven rack to the top middle and switch oven to broil. Divide soup into five small oven-safe bowls on a baking sheet. Top each with 6–7 grilled cheese croutons, ¼ cup shredded Gruyere, and ¼ cup shredded cheddar.

Melt the Topping: Broil for 2–3 minutes until cheese is bubbly and browned. Watch closely to avoid burning.

Serve: Let cool slightly, then garnish with chopped basil and serve warm.