Lettuce Soup with Fontina Gratin - Lidia

Ingredients

• 2 tablespoons unsalted butter
• 2 tablespoons extra-virgin olive oil
• 2 medium leeks, white and light green parts, halved and thinly sliced
• 2 garlic cloves, sliced
• 2 medium russet potatoes, peeled and cut into 1/2-inch cubes (about 1 pound)
• 2 quarts Chicken Stock, preferably homemade, or water (see here)
• 2 fresh bay leaves
• 1 teaspoon kosher salt
• 1 small head romaine, coarsely chopped (about 6 cups)
• 1 small head escarole, coarsely chopped (about 6 cups)
• Three 1/2-inch-thick slices country bread, lightly toasted
• 6 ounces Italian fontina, shredded