1Spread 1 side of each bread slice with butter. Spread 1 tablespoon pesto on unbuttered side of 4 bread slices; place buttered sides down in 12-inch skillet or grill pan. Top with beef, cheese and remaining bread slices, buttered sides up.
2Cook over medium heat 4 to 5 minutes, turning once, until bread is crisp and cheese is melted. Serve with pasta sauce.