[...] there was only so much “Foodie Chap” host and could do as the emcee of the BottleRock Napa festival’s Williams-Sonoma Culinary Stage when chef Jose Andres was joined by a trio of superstar bass players — Green Day’s Mike Dirnt, Metallica’s Robert Trujillo and Dave Matthews Band’s Stefan Lessard — plus Guns N’ Roses and Velvet Revolver drummer Matt Sorum, for a chaotic cooking demonstration on Saturday afternoon. Wielding a whole bone-in Jamon Iberico ham and a T-shirt that read “I Am An Immigrant,” the star Spanish American chef Andres took the stage and immediately ordered up a cocktail for his temporary line cooks. The musical supergroup, playing on bass guitars built out of pizza peels, kicked into an improvised jam that quickly evolved into what sounded like the “Seinfeld” theme song. Dirnt made himself useful by grating generous portions of black truffle over cheese and bread, making some very expensive sandwiches that the entire crew somehow neglected on the grill long enough to burn. “Do you guys want more bass?” Mayclem asked the bewildered crowd, leading to another boisterous jam session of less than platinum standards. To close the whole thing out, Trujillo’s 12-year-old son — who not only plays in Sunday openers the Helmets, but is also a member of the reconstituted lineup of Korn — took the stage for a pizza peel bass solo with one of the charred sandwiches stuffed in his mouth.