Empalme means 'junction' or 'splice', which is exactly what it is: two tortillas joined by a layer of beans.
Two corn tortillas are rubbed with pork lard, sandwiched around refried beans and salsa (sometimes with chorizo or cheese), then warmed crisp on a comal or over charcoal and eaten by hand.
Why it's made this way: It comes from General Zuazua and the other Valle de las Salinas municipalities just north of Monterrey, such as Marín, Ciénega de Flores and Salinas Victoria.