One of these, which has since become a favorite is Primavera Trujilla, located on the Belgrano/Nunez border at 1627 Roosevelt. There's two Peruvian restaurants on this short block - Primavera Trujilla is the yellow one.
It's small interior holds a dozen or so closely packed tables that are nearly always occupied. Both times I've been I've gotten a table right away, but there were only one or two more left. The interior is plain and simple with miscellaneous Peruvian decorations and tapestry tablecloths.
The menu is about 50/50 seafood and other dishes. The seafood is quite good for B.A. standards, especially ceviche considering it's raw! The mixed ceviche is delish with mussels, calamari and fish in a perfect lime and cilantro sauce. The aji de gallina is another delish dish, especially if you are a non-seafood-eating-freak. Even if you are normal, on a cold day the creamy sauce and big chunks of chicken make for a hearty meal.
[As an aside I hate eggs and chicken together; it seems unnatural and creepy. But as they say "you get what you get and you don't get upset."]
Ale, the adventurous Argie eater that he is, got the Lomo dish, i.e. steak with peppers and onions. It was good, though the equivalent of getting pasta with butter from a French chef. The french fries were crunchy outside and delicious though!
They also have a killer lunch special. You better get it while you can aka before they adjust the price for inflation. Midday from Monday through Friday they have 9 different options (including aji de gallina) ranging from 30-36 pesos including a water or soda. It's almost like the good old days, before Cuban style economics took over.... almost.