Ate at Mandoline (3rd and Chestnut) last night with a group of people before a black-tie event. We were significantly over-dressed for the restaurant, but on a Tuesday night it was empty enough for that not to matter.
The menu was small, but fantastic. Appetizers included three different salads, pasta dishes, and steamed mussels (which I had, and which were amazing). Entrees ranged from Israeli couscous with spring vegetables to roasted chicken to a filet mignon, and prices were very reasonable (about on par with other Philly BYOBs). I had the grilled tuna, which was cooked perfectly (hot on the outside, cool and pink at the center) and served over the best mashed potatoes I'd ever had. (Do be careful, though: they use whole cloves of roasted garlic in the potatoes, so you might be in for a surprise.) Others at the table ordered the chicken, and two different pasta dishes.
There was a large dessert selection available, but dinner left us so full that we didn't dare order anything else.
The waitress was also fantastic (I wish I'd caught her name). At one point, she overheard some of us at the table discussing how difficult it was to resist eating bread while dining out during Passover, and she brought us a basket of warm matzoh along with the bread basket (even bringing along a pat of butter because "matzoh can be bland sometimes").
The restaurant was nearly empty, and I hope that's only because it was a Tuesday night; the food was too good for this place not to be well-attended. It's a great place to go on a date, or with friends.