Panino Di Prosciutto E Fontina

From Giada De Laurentiis; Everyday Italian

2 to 4 slices (3 ounces total) fontina cheese
2 slices (1/2-inch-thick) rustic white bread
2 paper-thin slices red onion (optional)
Salt Freshly ground black pepper
6 fresh baby spinach leaves
1 to 2 paper-thin slices (1/2-ounce) prosciutto
.2 to 3 teaspoons olive oil

Place 1 to 2 slices of fontina atop 1 bread slice. Top with the onions. Season with salt and pepper. Then add spinach and prosciutto. Add the remaining slice(s) of fontina. Top with the second bread slice. Brush both sides of the sandwich with the oil.
Heat a grill pan over medium-low heat. Grill the sandwich until the bread is golden brown and the cheese melts, pressing down with a metal spatula or grill press, about 4 minutes per side.