B'fast -- Pani BA (at foot of Recoleta mall but separate entrance outside)...super cute. Waffles (without maple syrup, as they don't seem to have that anywhere in BA), eggs. wonderful tea/coffee, and a place you can sit and hang for hours.
Dinner: I Latina (Palermo SoHo) -- absolutely divine and amazing menu. Owners are a Columbian family -- chef is inventive (but not too crazy) and the quality of everything was great.
Another dinner place is Osaka (Palermo Hollywood) -- excellent sushi, but many of the "standards" from the US aren't available in BA, so interesting substitutions. The place is very hip, and the drinks (pisco sours) are creative and delicious. We all shared, but the ceviche sampler (the "digestion") and the lomo (Kobe-type beef) teriyaki were particularly great.
Sotto Voce in Recoleta is also terrific -- we went for lunch but I'm sure it's also good for dinner. Lovely chicken piccata, salmon paillard, homemade pasta, breads, and good vegetables. More of a business-type lunch, but delicious.
The dinner at the Park Hyatt Duhau was also fantastic. We had their asado (grilled) sampler -- with lamb and multiple cuts of beef. Nice side dishes and excellent service. Pretty room, too. (Very quiet, though.) Cool "cheese room" and great wine list.
Arkakao -- (fairly new and casual) We went for their "artisan" ice cream, but the food turned out to be great, too. Open for lunch and dinner. We had caprese salads, chicken limone/piccata, and then amazing dark chocolate ice cream and banana sorbet.
Other ice cream -- Freddo and Persicco (local chains but really really good) and Bufala (new -- on Las Heras in Recoleta). Yummy!
Definitely a great food city. Enjoy!