Nestled between wholesalers selling cosmetics, fruits, and electronics in the Union Market area, there's a metal gate along a tall wooden wall with nicely manicured flowers out front. Beyond it, you'll find chef Nick Stefanelli's oasis of an Italian restaurant, Masseria, in what used to be a concrete-walled produce warehouse. The former Bibiana chef will open the restaurant on July 21 with a limited menu and limited seatings. The official grand opening is slated for Aug. 4.