The ever-experimental folks at Petaluma’s Once Upon a Slush have been steadfastly adding intriguing items to the idiosyncratic American Alley shop’s menu, working hard to spread the word that you can pick up more than just a quick cold dessert at the whimsically decorated downtown location. In addition to a wild array of slush and soft serve flavors, you will also find hotdogs (uniquely served on a buttered lobster roll), supremely melty grilled-cheese sandwiches, hot buttered “movie style” popcorn and a rotating array of hot and steamy soups…