For a great appetizer that can be served with carmelzied onions or diced bacon, check out Chef Laurent Tourondel's delicious popovers.
Place the popover pan in the oven. Heat the oven and pan to 350 degrees. Gently warm the milk over low heat and set aside. Whisk the eggs until frothy and slowly whisk in the milk (so as not to cook the eggs).
Set the mixture aside. Sift the flour with the salt. Slowly add this dry mixture to the egg mixture and gently combine until mostly smooth. Once combined, remove the popover pan from the oven and spray with non-stick vegetable spray.
While the batter is still slightly warm or room temperature (definitely not cool), fill each popover cup ¾ full. Top each popover with approximately 2 ½ Tbsp of the grated gruyere.
Bake at 350 for 50 minutes, rotating pan half a turn after 15 minutes of baking, until golden brown. Remove from the oven, remove from the pan and serve immediately.