A small Yorkshire pudding is the answer. Basically a very puffy, nearly hollow muffin. That’s the ideal at any rate, since popovers have a notoriously high failure rate, and all too often resemble actual muffins for their compact size and density. They don’t “pop over” in other words…overflow the bounds of the small cups they’re baked in.
Interestingly, they originate from a thin batter, a batter that is very similar to pancake batter though it’s treated a bit differently. For one it’s agitated a whole lot — popover batter is usually whipped up in a blender or a food processor. That’s a major no-no in the world of pancakes, as lots of working it makes a griddles cake tough.
But it’s essential in the realm of popovers. Without plenty of activated gluten the walls of these big, edible bubbles won’t stretch, which means the steam that builds up inside of them will leak out through cracks, and the explosive rising popovers require will be over before it even begins. So if you can forget everything you know about how to treat a pancake batter, odds are you’ll be able to create an outstanding popover.