(From left) Strawberries and cream gelato; peanut butter ice cream sandwich; dirty mint chip. Brian Leatart/Courtesy of Houghton Mifflin Harcourt hide caption

itoggle caption Brian Leatart/Courtesy of Houghton Mifflin Harcourt

Thousands of students from around the world flock to courses near Bologna, in central Italy, at the headquarters of Carpigiani, the leading global manufacturer of gelato-making machines. Giuseppe Cacace/AFP/Getty Images hide caption

itoggle caption Giuseppe Cacace/AFP/Getty Images

The Smitten Ice Cream shop in the Hayes Valley of San Francisco serves fresh ice cream with one novel ingredient: liquid nitrogen. The shop is located inside of a repurposed shipping container. Alan Greenblatt/NPR hide caption

itoggle caption Alan Greenblatt/NPR