I think Yorkshire Pudding would be closest to a popover in the US. As one of the PPs mentioned, the batter is a lot like pancake batter--but the difference is, the Yorkshire Pudding is baked at a very high temperature in the oven, in pre-heated pudding dishes (I use a muffin tin for individual puddings), so it really puffs up. They are frequently made with the fat drippings from a roast beef. They are very light, and mostly hollow inside.