Clean the leeks well, cut the white part of each leek into 2-inch strips, and discard the green parts.

Heat the chicken broth in a large saucepan.

Sauté the leeks in the butter until they are golden brown in color. Add to the hot broth and cook, covered, for 30 minutes.

Meanwhile, make the crostoni: Sauté the garlic in the oil until lightly browned; remove and discard. Add the bread to the oil and toss well until each cube is coated; add the salt and pepper. Place cubes in a baking pan in one layer; bake in a 400 degree oven for 10 minutes.

Place a few crostoni in each of 4 soup bowls; pour the soup over the bread cubes, and serve hot.