Preparation

• In a medium bowl, toss the arugula with 1 Tbs. oil, the vinegar, 1/8 tsp. salt, and 1/4 tsp. black pepper. Let sit for 5 minutes to wilt slightly. Set 4 slices of bread on a cutting board. Gently rub both sides of each piece of bread with the garlic. Top each slice of bread with 2 tomato slices and sprinkle evenly with 1/2 tsp. salt. Layer the prosciutto, Fontina, and arugula mixture over the tomatoes. Rub both sides of the remaining 4 slices of bread with the garlic and set these slices, garlic-rubbed side down, on top of the arugula. Discard the garlic. Brush the outsides of the bread slices with the remaining 2 Tbs. oil.
• Heat a panini press according to the manufacturer’s instructions. (Alternatively, heat a nonstick grill pan over medium heat.) Put two of the sandwiches on the press, pull the top down, and cook until browned, 5 to 7 minutes. (If using a grill pan, put a heavy pan on top of the sandwiches and cook for roughly the same amount of time, turning the sandwiches over once.) Cook the remaining sandwiches in the same manner. Cut in half and serve.