Preheat oven to 350 degrees. In a medium bowl, mash 1 garlic clove with the salt to form a smooth paste. Add bread cubes, and toss to combine. Spread cubes in a single layer on a rimmed baking sheet. Bake until crisp and golden brown, about 20 minutes, turning once.
Make the vinaigrette: In a small bowl, mince remaining garlic clove with the anchovy, if using, to form a smooth paste. Whisk in lemon juice, Worcestershire, mustard, and the pepper. Slowly whisk in the oil.
In a large serving bowl, toss lettuce with vinaigrette and reserved croutons. Serve immediately, garnished with shaved Parmesan.