Preheat oven to 450 degrees F, making sure the oven rack is in a low position. Place the popover pan on top of a cookie sheet or pizza stone, and put into the oven while it is preheating.
Place the uncracked eggs into a medium bowl of very hot water. Let them sit in the warm water for 10 minutes. (Add more hot water after a few minutes.)
Put the milk into a pyrex measuring cup, and place into the microwave for about 40 seconds, long enough to slightly warm up the milk.
When the eggs have warmed up, beat them with a whisk or egg beater until frothy. Add the warmed milk and the salt and whisk them together until combined.
Add the flour to the wet ingredients, and whisk until the batter is just smooth. Stir in the melted butter quickly. Let the batter rest for about 10 minutes.
Take the popover pan out after the oven has heated to 450 degrees and spray each cup with Pam cooking spray.
Pour the batter into the hot prepared pan, dividing the batter between the popover cups. Each cup should be at least 3/4 of the way full, or more. Sprinkle on optional herbs or grated cheese.
Put the pan back into the oven, onto the cookie sheet or pizza stone. Do NOT open the oven door until the popovers are done. Bake the popovers for 20 minutes at 450 degrees F, then reduce the heat to 350 degrees F. Bake another 15-20 minutes. The popovers will rise and become very golden brown.
Serve immediatley with butter or jam.