It's named after Ramón Barros Luco, president of Chile from 1910 to 1915, who is said to have ordered the same steak-and-cheese combo so often that it took his name.
Thin-sliced grilled beef is melted together with a slab of cheese inside a soft bread roll, served hot from Santiago's classic 'fuentes de soda' sandwich counters. It's eaten standing at the counter or wrapped to go.