Mauro.it Il ristorantino Italiano in Belgrano, where a plate of pasta is compulsory! They have around 10-15 sauces, and at least one with fish (but honestly I can't remember which and I didn't try it). You pick the sauce, Mauro picks the pasta format that best match it.
I had tagliatelle ai funghi and my husband had an interesting linguine con pesto e gorgonzola. As a starter, we had a bruschetta and a burrata.
His tiramisù is the best I ever had in Buenos Aires, Mauro does the mascarpone himself (showed me the big bowl, offered me a sample) and it is the real deal.
We spent around 500 ARS drinking water. The place is not cheap by Argentinian standard, but the food is good. Mauro also appeared in some TV shows and there are many pictures of celebrities (both Italian and Argentinean) on his walls. He does pretty basic stuff, the kind of food you would eat at an Italian home.
I don't have much experience with eating Italian food in Buenos Aires, so far.
The only other place I tried was
Gulie in Palermo, but we arrived late and they only served cold food, so we just had a burrata with tomatoes and salad, a tiramisù and a coffee. Avoid the tiramisù, which is not so much of a thing (of course, impressive compared to the Argentinians' version). The coffee was served bringing the moka directly on the table, which was nice. The burrata was more of a mozzarella, I liked Mauro's more. But anyway, a burrata in Argentina... what do you expect?! (at least, for those who have tried a genuine burrata from Puglia...)