The Food Timeline.com...
"Popover. A light, hollow muffin made from an egg batter similar to that used in making Yorkshire pudding. The name comes from the fact that the batter rises and swells of the muffin tin while baking...In American Food (1974), Evan Jones writes: Settlers from Maine who founded Portland, Oregon, Americanized the pudding from Yorkshire by cooking the batter in custard cups lubricated with drippings from the roasting beef (or sometimes pork); another modification was the use of garlic, and, frequently, herbs. The result is called Portland popover pudding, individual balloons of crusty meat-flavored pastry." Most popovers, however, are not flavored but merely set in buttered muffin tins. They are served a breakfast or with meats at lunch and dinner."
---Encyclopedia of American Food and Drink, John F. Mariani [Lebhar-Friedman:New York] 1999 (p. 249)