These popovers really are big. The recipe is from the 1940's and were served in Boston restaurants. They're buttery, crisp, and wonderful. This recipe produces the lightest tallest popovers using ovenproof china custard cups. Source: Unknown
Set oven rack in middle position. Preheat oven to 375. Coat eight 8 oz. ovenproof china custard cups with vegetable spray. Put custard cups on foil lined jelly roll pan; foil should be shiny side up.
Whisk eggs in large bowl til frothy. Add milk and cooled, melted butter and whisk to combine. Whisk in flour and salt. There will be some lumps. Fill each custard cup with 3/4 cup batter.
Bake popovers on jelly roll pan about 1 hour or til tall and buttery brown. Don't open oven door while popovers are cooking.
Remove pan from oven; leave oven on. Puncture nick of each popover on four sides to allow steam to escape. Return pan to oven and bake popovers 10 minutes more. Remove popovers form oven and turn out of cups. Serve at once with butter or jam.
Popovers are best eaten the day they are made, but leftovers may be stored in a plastic bag at room temperature and reheated the next day in the oven. They will be neither as light nor as crisp as the day they were fresh, but they will still be tasty.