Popover pans are a special baking pan used to make the pastry
known as a popover. They are deeper than a cupcake tin, and this
forces the dough to go up, making a beautiful puffy top to the
pastry.
Popovers normally use milk, flour, sugar, baking soda to help
rise the cake, as well as eggs, butter, and a bit of salt. The
popover pan itself is not an ingredient - it is a pan that helps
form the popover into the right shape.