Heat oven to 450°F. Place a 12-cup muffin tin on the center rack to preheat.
Divide the oil or drippings among the muffin cups. Return the pan to the oven until the fat is sizzling hot, about 5 minutes.
Whisk the eggs in a bowl until lightly foamy. Whisk in the milk.
Sift in the flour and salt. Whisk just until smooth; a few tiny lumps are fine. Let the batter rest 5–10 minutes.
Carefully pull the hot pan from the oven. Quickly pour the batter into the cups, filling each about halfway.
Bake 20–22 minutes without opening the door, until puffed and deeply golden.
Serve immediately while crisp. They will settle slightly as they cool.