Grilled Fontina and Prosciutto Sandwiches with Black Pepper-Thyme Butter

Mix first 5 ingredients in small bowl. Place 6 bread slices on work surface. Spread 1 teaspoon butter mixture over each bread slice. Top with single layer of cheese and prosciutto. Top with remaining bread slices. Spread 1 teaspoon butter mixture over top of each sandwich.

Heat 2 heavy large nonstick skillets over medium heat. Add 3 sandwiches buttered side down to each skillet. Spread remaining butter over sandwiches. Cook until bottoms brown, about 3 minutes longer. Turn sandwiches over. Cook until second sides brown and cheese melts, about 3 minutes longer. Transfer sandwiches to work surface. Cut each diagonally in half. Transfer to plates and serve.