
In a large skillet over medium heat, melt butter. Add shallots and cook until soft, 3 to 4 minutes. Add thyme and cook until fragrant, 1 minute more. Season with salt and pepper. Heat oven broiler to medium.
Add tomatoes and heavy cream and bring up to a simmer. Stir in parmesan until melted, season with salt and pepper, then turn off heat and top with mozzarella. Broil until cheese is golden and tomatoes are beginning to char, 2 to 3 minutes.
Garnish with basil and serve hot with bread on the side.