How to Make It
In a small bowl, combine the cheeses. Spread the cheese on the bottoms of the ciabatta rolls, top with 2 arugula leaves and close the panini.
Set a large cast-iron skillet or griddle over moderately high heat. Arrange the panini in the skillet and weight them down with a smaller pan. Cook the panini until the outside is crisp and the cheese is melted, 3 minutes per side. Cut the panini in half and serve at once.