Mix the batter by volume: Crack 3 eggs into a measuring cup and note the volume. Use that same amount of flour and milk. Whisk eggs + flour until smooth, then whisk in the milk. Batter should pour like loose whipping cream.
Rest: Let sit 2 hours on the counter (or overnight in the fridge).
Heat the pan: Set oven to 450°F (fan off). Heat an empty muffin pan (or 6 ramekins) for 10 minutes.
Add the oil: Add 2 tbsp oil per cup and heat another 10 minutes until lightly smoking.
Bake: Work fast — fill each cup halfway to ⅔ full. Bake 10–12 min at 450°F, then reduce to 350°F for another 10–12 min.
Cool: Move to a rack so the bottoms stay crisp. Serve hot.
