I'm sitting here eating a BBQ beef Bahn Mi from Thai Binh market, wishing it were two and reading about Clem and Ursies Lobster Roll that I will try early next week when I'll be in Provincetown. It got me thinking about sandwiches that I've had that changed my life. OK... so I need a life. This said, every once in a great while, a single bite makes the Earth move and the stars twinkle. On my short list are the Mufellatta from Central Grocery (New Orleans), the handcut pastrami from Katz (NY) and a charcoal grilled pork souvlaki from a little stand in Athens that had been there since WWII. Are there others out there that you can share? Even better if they are in or within striking distance of Boston.