Move the oven rack to the lowest possible position. Preheat oven to 425° F. Liberally grease the popover pan, custard cups or every other cup of a muffin pan with butter or cooking spray.
Be sure to have milk and eggs at room temperature before proceeding. Combine all ingredients in a blender and mix until smooth. No lumps!
For the popover pan or custard cups: pour ⅓ cup batter in each.
For the muffin pan: pour ¼ cup of batter into every other cup.
Bake for 25 minutes WITHOUT OPENING THE DOOR!
Lower the oven temperature to 350°F and bake for another 15-20 minutes (FYI, mine were done in 10 minutes, but I'm telling you what the recipe says).
Remove from oven and cut a slit in the top to allow the steam to escape. Serve immediately.
Notes
The right pan is critical for these. If you do not have a popover pan (affiliate link) you can use every other cup of a 12 muffin pan (you'll want two) or ¾ cup capacity custard cups on a rimmed baking sheet with plenty of room in between