We picked up the habit of tortilla in Barcelona, then worked on it in New York. The open-faced omelet, which is what tortilla means in Spain, can be served either at room temperature, as we do at Mangia, or hot, which you can do at home. Just bring the skillet straight from the broiler to the table, with the ciabatta in a basket alongside. And if ciabatta is not available, substitute a large baguette.