1⁄2 cup extra-virgin olive oil
2 cloves garlic, peeled and finely chopped
2 leeks, white and light green parts only, washed and finely chopped
9 cups puréed peeled Italian tomatoes
3 cups veggie stock
9 slices (¾”-thick) stale, unsalted Tuscan bread (about 1 lb.), halved
2 tbsp. chopped basil leaves
Kosher salt and freshly ground black pepper, to taste
Heat ⅓ cup of the oil in a large wide pot over medium heat. Add garlic and cook until light golden, about 2 minutes. Reduce heat to medium-low, add leeks, and cook, stirring often, until very soft but not browned, 15–20 minutes. Add the tomatoes and chicken and beef stocks and stir to mix well. Increase heat to medium-high and bring soup to a boil. Then reduce heat to medium-low to maintain a simmer and continue to cook, stirring occasionally, for 30 minutes.
Remove the pot from the heat. Add the bread, pushing it into the soup with a wooden spoon until each piece is submerged. Add the basil and stir gently to combine. Cover the pot and set it aside to let the bread soak until completely softened, about 30 minutes.
Uncover the pot and whisk the soup vigorously until the bread breaks down and the soup resembles porridge, 4–5 minutes. Season to taste with salt and pepper. Gently reheat soup over medium heat. Ladle the soup into warm bowls and drizzle with remaining olive oil.