P.J. Waters made his name at Via Matta with his irresistible “mascarporeos,” whipped mascarpone with delicate chocolate cookies. At upscale Radius, he’s let his imagination soar with innovations such as deconstructed carrot cake with mascarpone, pickled carrot salad, and a shot of spicy coriander chai and the Cinema Paradiso, a sampler of crunchy chocolate, cherry slush, and buttered popcorn ice cream. This is no standard sugar fix. Waters’s creations boast a delicate balance of creativity, whimsy, and old-fashioned, sock-it-to-you sweetness.