Pop star Joe Jonas has a sweet tooth.

The 21-year-old rock icon spiced things up as a guest judge on Wednesday night's Top Chef All-Stars "quickfire challenge." He tasked the 17 contestants with whipping up a midnight snack that could satisfy 150 hungry grade school children who were having a Night at the Museum-themed slumber party at the American Museum of Natural History in New York City. The challenge: make a dish that requires no utensils or plates, Jonas explained. "And you have thirty seconds," he said, receiving expressions of abject horror in response before he assured he was just kidding about that last part.

Jonas happily tested all 17 of the delectable treats, most of which were made sugary with the kids in mind. In the end he picked two snacks — Tiffani Falson's ambitious amalgam of a Sno Ball, Moon Pie, and Rice Krispy Treat, and Spike Mendelsohn's carrot potato chips with mascarpone dip. He made Mendelsohn sweat a bit before picking his dish, however. "Hm, I've never had marshmallows with chips before," Jonas said, eliciting a nervous smile from the competitor.

The snacks the chefs came up with varied as much as their reactions to Jonas. "They're rock stars; they're world-famous teenage heartthrobs," Mendelsohn said, while Antonia Lofaso talked about what a "huge Jonas Brothers fan" her daughter is. "She's going to be so unbelievably excited that I was just in the same vicinity as [Joe]," she said. Contestant Dale Talde had a different reaction, however. When he walked into the kitchen to see Jonas standing there with host Padma Lakshmi, he "had no idea" who the star was, he later said. "I thought he might be a pastry chef." —KIMBERLY STEELE