Heat the olive oil in a large saucepan and add the chopped onion. Cook on low heat for 5-6 minutes until softened. Add garlic and sweet potato, then cook for another minute. Add tomatoes, stock, tomato puree, and sugar. Bring to boil, then simmer for 20 minutes, stirring occasionally.

Preheat a griddle pan on high heat. Spread shredded cheese on two slices of bread and top with remaining slices. Brush outside of sandwiches with olive oil. Grill until dark grill lines appear, about 3-5 minutes per side. Remove, chop into cubes, and set aside.

Once the soup is cooked, turn off heat and blend with an immersion blender until smooth. Stir in the heavy cream and season with salt and pepper.

Divide the hot soup into bowls and top with the cheese toast croutons. Serve immediately.