Preheat the oven to 220°C / 425°F / Gas 7
Put 1 teaspoon of oil, beef dripping, or vegetable oil into each hole of a muffin tin
Place the tin in the oven until the fat is very hot
In a bowl, whisk together 140 g plain flour and a pinch of salt
Add 4 eggs and 200 ml milk
Whisk until smooth and lump-free
Leave the batter to rest for 10 to 30 minutes if possible
Carefully remove the hot tin from the oven
Quickly pour the batter into the hot holes, filling each about halfway
Return the tin to the oven immediately
Bake for 20 to 25 minutes without opening the oven door
Remove when puffed up and golden brown
Serve immediately