Fontina cheese is rich and creamy, making it a perfect melting cheese. Although you can use the more readily available Danish Fontina, I highly recommend you seek out Italian Fontina—it's a far more flavorful cheese.
- 2 teaspoons olive oil
- 1 large leek (about 6 ounces), white and light green parts thinly sliced, then rinsed and patted dry
- ½ teaspoon kosher salt
- ¼ pound pancetta, cut into 4 paper-thin slices (or buy it presliced)
- 2 tablespoons butter, at room temperature
- 8 slices sourdough bread, ¼ inch thick (or for a nuttier flavor, use rye)
- 6 ounces Italian Fontina cheese, coarsely grated
Heat the oil in a large nonstick skillet over medium heat. Add the leeks and cook, stirring occasionally, until they are limp but not brown, about 7 minutes, then add the salt. Transfer the leeks to a bowl and let cool.
Increase the heat to medium-high and add the pancetta to the skillet. Cook for 3 minutes, or until brown. Turn and cook about 2 minutes more, or until the pancetta has turned deep golden brown. Transfer the pancetta to a plate, and when cool enough to handle, chop it into bite-size pieces. Wipe the skillet with a paper towel, but do not wash it.
To assemble: Butter one side of each slice of bread. Place 4 slices on your work surface, buttered side down. Distribute the cheese evenly over the 4 slices, followed by the leeks and pancetta. Place the remaining 4 bread slices on top, buttered side up.
STOVETOP METHOD: Heat the same skillet over medium-high heat for 2 minutes. Put the sandwiches in the skillet (in batches if necessary), cover, and cook for 2 minutes, or until the undersides are golden brown and the cheese has begun to melt. Uncover, and turn the sandwiches with a spatula, pressing firmly to flatten them slightly. Cook for 1 minute, or until the undersides are golden brown. Turn the sandwiches again, press with the spatula, and cook for 30 seconds, or until the cheese has melted completely. Serve immediately.
SANDWICH MAKER METHOD: Preheat the sandwich maker. Follow directions for sandwich assembly, and cook according to the manufacturer's instructions.
GAS GRILL METHOD: Brush the grill rack with oil and preheat the grill to medium-high. Follow directions for sandwich assembly. Put the sandwiches on the grill and follow directions for the stovetop method.