A reasonably bright chimpanzee could be taught to make a faultless key lime pie: There's one immutable method, and it allows for no deviation. The recipe involves a can of condensed milk, a couple of eggs, a box of graham crackers, a stick of butter, and a handful of key limes. To see so many reasonably bright human beings in local restaurant kitchens floundering around with meringues and preformed crusts, Persian limes -- or worse -- bottled lime juice, whipping cream, and God-knows-what-all, is to witness the awful human compulsion to fiddle with what ain't broke. That being said, exceptions do exist. The pie-in-the-sky concoction dreamed up by pastry chef Gus Hernandez at River House is certainly one. His "key lime pie baked Alaska" is a delicious joke composed of a Brazil-nut graham cracker crust, a tower of sweet limey mousse, a rakish chapeau of browned Italian meringue, and many decorative swivels and swirls of berry coulis. That you can sit outdoors at a table under the stars to eat this pie between the glittering lights of two august mansions and the lazy New River makes variations like this one seem necessary.