Lingua franca: There's an appetizer on the menu at Da Marco that I'm willing to bet is not available at any other restaurant in Houston. In fact, one of the ingredients is so rare in the United States that I doubt it's available anywhere on this continent. The dish is Lamb Lingua with Mostarda($10), but the rarity is not the tongue, it's the accompaniment. Mostarda is a preserve of many different kinds of candied fruit soaked in a syrupy sweet hot mustard sauce. The condiment comes from the northern Italian city of Cremona (the home, incidentally, of famous violin maker Antonio Stradivari) and dates back to Roman times.