Once again, Chinatown dim sum let me down Saturday, but Mario saved the day. I went to Sweet n Tart at 20 Mott Saturday morning hoping to find that elusive LA-quality dim sum. Instead I found a sweet but incompetent staff and mediocre food. The turnip cakes were greasy and soggy, the stuffed eggplant was just okay, and the steamed seafood and asparagus dumplings were slightly mushy with no distinct flavor. I also ordered sesame balls, and when they still hadn't come after I was finished with everything else had to ask twice more to get them. They were crusty and dry (as if they had been sitting under a heat lamp, maybe?) and I only ate one of the three - an occurrence as rare as a useful review in the Zagat guide. Luckily I made a better choice for dinner. After several tries over the past few months I finally got a seat at the bar at Babbo, and it was wonderful. The lamb's tongue salad, topped by a lightly poached egg, was a study in contrasts and one of the richest appetizers I've ever had. My main course, a veal and pancetta roulade, made up for all the times I've been served dry veal. It melted in the mouth like a slow-cooked roast. A flourless hazelnut and chocolate cake was just sweet enough. From the depths of inedible sesame balls to the heights of sublime Italian, all in six hours and one subway stop.