Buenos tardes, amigos de Chowhound.
I recently found the best tortas I have ever eaten, in Mexico City.
Tortas La Castellana has been around since 1946. I visited their shop in Polanco. If you're at the Plaza Moliere where the large Palacio de Hierro store is, you can find this shop on the right side of the building just across the street (what I mean is that if you're facing Plaza Moliere, walk to its right and cross the street - it's right there).
They have a full ranne of these amazing Mexican sandwiches. My favourites are the bacalao (Mexican cod fish), pulpo (tender octopus) and pierna (meat leg).
These sandwiches are so good they're impossible to describe. At around 30 pesos (around three dollars) per large sandwich, it's a steal.
Very clean restaurant, very safe area. Can't go wrong.