These additively delicious, overstuffed, little sandwiches are a popular snack in Central Mexico. Traditionally, tortas are made with bolillos (bobbin-shaped bread rolls) or sometimes teleras (flat bread rolls) both are made from the same French bread type dough. The only difference is the shape of the roll. French bread rolls are a good substitute, as are sourdough rolls. The idea is to use a crusty roll with a soft interior. In making the torta, one starts by cutting the roll horizontally, then removing some of the crumb to create a hollow for the filling. These sandwiches hold up well for several hours, without getting soggy, which makes them good for parties and picnics. The inspiration for this recipe comes from the delicious tortas I've eaten in Mexico City, combined with some useful information in Diana Kennedy's book: "The Art of Mexican Cooking, Traditional Mexican Cooking for Aficionados".