Introduced in the 1930s, when cast-iron skillets were more commonly found in kitchens than baking pans, the upside-down, or skillet, cake has survived eras of modernization to remain a beloved dessert. Today, Martha puts a seasonal twist on this old-fashioned favorite, eschewing the classic pineapple for sweet and juicy Bartlett pears—large, bell-shaped fruits with smooth, yellow-green skin.