This crustless cheesecake, baked in a very hot oven so the top caramelizes but the inside remains soft and jiggly, came out of San Sebastián, Spain, in the 1990s. Some elite American chefs started making versions, and two years ago it slipped into more mainstream food culture. Chefs in New York and San Francisco have dedicated themselves to perfecting the cheesecake; it is now a soft-serve flavor in Singapore and may become the birthday-cake or cookie butter flavor of 2021.