On rimmed baking sheet, toss together garlic, onion, potato, butter and 1/4 tsp (1 mL) each salt and pepper. Roast in 450 degrees F (230 degrees C) oven for 25 minutes, stirring twice, or until golden and softened.
Meanwhile, in a pot combine tomatoes, stock and basil; bring to a boil over high heat. Add vegetables. Reduce heat; boil gently for 10 minutes. Puree until very smooth. Return to pot (if necessary) over medium-low heat. Stir in cream; season with salt and pepper. Heat, stirring often, until steaming.
On baking sheet, broil baguette slices until lightly toasted. Turn over and sprinkle with cheese; broil until cheese is melted.
Lade soup into warmed bowls; float crouton on top of each serving.