Heat butter and olive oil in large saucepan. Add onion and garlic, and sauté until golden brown.

Grate tomatoes with a hand grater. Add grated tomatoes, thyme, water and milk to the pot and cook for one hour.

Cool slightly and blend using an immersion blender.

Add heavy cream, salt, pepper, and sugar. Feel free to add water or milk to achieve the desired consistency.

Preheat oven to 375 degrees Fahrenheit (190 degrees Celsius).

Slice rolls or baguettes into half-inch (one-centimeter) slices. Top each slice with a cube of cheese and bake in the oven for a few minutes, until the cheese is melted and golden.

Serve on top of soup and garnish with basil leaves.