Popovers are an American variation on the British Yorkshire Pudding. It is an eggy, buttery pastry that is filled with air. Though popovers are still served here with beef and gravy, they are also served for breakfast with jam.
Growing up in the Southwest, I had never heard of popovers until I was newly married and visiting my In-laws in New England. At a Sunday lunch I experienced the rich, yet light and airy, deliciousness of popovers drizzled in prime rib fat. My mother-in-law scooped out the drippings and drizzled them over the tin before heating the pan and filling it with batter and while you can do this, I prefer to coat it in butter. The method of heating the pan until it is 'hissing hot' before the batter is put in allows the batter to steam internally which causes it to rise and puff up. If your pan is too cold you will not get this affect. But also do not heat it so long that you burn the butter.
Popovers have a poshness that make them a wonderful accompaniment to dress up any beef dinner. And though you can bake popovers in a muffin tin, authentic popovers are baked in special baking cups that are narrow and deep so that the pastry fills with air and rises tall. This gives them their wonderful texture and distinctive appearance. If you choose to bake popovers in a muffing tin you will get a lower the rise, which means the pastry will be denser, and the pastry will have less of a hollow center.