Is the only difference between popover and yorkshire pudding the addition of beef fat to baking vessel?
The interiors are moist with lots of open steam pockets for butter and jam. They should be puffy. Dry on the exterior. If they slumped in the middle, then they didn't rise properly, but they would still be good.
Hi! Yes on the vessel being preheated, it makes sure they "pop" and I think they are essentially the same as Yorkshire pudding with beef fat being the variable
Oh and I like this basic recipe - I have made it several times - the directions get you to the perfect popover!
I've always preheated the pan. The insides should be a bit wet.