Pato Rodriguez is the founder of Las Chicas de la Tres—the “tres” referring to the number of the loading dock where her food stall is situated at the Central Market of Buenos Aires. Her food is as good an introduction as any to the ethos of Argentine cuisine, which is usually associated with beef but, according to Ms. Rodriguez, is all about “mucho queso.” And she means it: Her signature potato tortilla, three to four inches deep and cut like a melty pie, makes one want to say adios to the diet in favor of the “mozzarella effect” that Ms. Rodriguez sells so convincingly.