Step 1

Preheat oven to 450 degrees F.

Step 2

Toss onions, oil, salt and pepper in a 9-by-13-inch pan. Roast the onions, stirring once or twice, until starting to brown, about 20 minutes.

Step 3

Stir in tomatoes and 1/2 cup garlic and continue roasting, stirring once, until the tomatoes are falling apart and beginning to brown in spots, about 20 minutes more.

Step 4

Transfer the onion-tomato mixture to a large saucepan. Add broth. Bring to a simmer over medium-high heat. Remove from the heat and cover to keep warm.

Step 5

Meanwhile, place bread on a large baking sheet and bake until toasted, about 10 minutes. Rub both sides of the toasted bread with the halved garlic clove. (Discard remaining garlic.)

Step 6

To serve, place a piece of toasted bread in a shallow soup bowl. Ladle about 1 cup soup over the bread. Sprinkle with basil and cheese and serve immediately.