From the directions that came with my popover pan (or follow recipe on pg 631-632 in Joy Of Cooking 1975 edition).
Preheat over to 400 F.
Blend popover batter:
1.25 C flour (I use a blend of all purpose and whole wheat pastry flours, roughly half and half)
1/4 tea salt
1.25 C milk
1 TB butter, melted
Preheat popover pan in over for 2 minutes.
Use 2TB of butter pats to put in hot popover pan, then add popover batter. You could alternatively grease the pan .
Fill popover cups half-full with batter, bake at 400 F for 20 minutes. Then reduce oven temp to 300 F and bake another 20 minutes.