Shake Shack’s debut is the latest in a string of blockbuster IPOs from trendy restaurant chains that cater to younger and more affluent diners willing to pay a bit more for fresher and higher quality food. Growth-hungry investors are hoping to replicate the red-hot run of industry darling Chipotle Mexican Grill (CMG.N). Its IPO followed the successful listing two months ago of fellow premium burger seller Habit Restaurants (HABT.O).