Put the eggs into a mixing bowl and add the flour. Whisk to a smooth paste then gradually add the milk and water, whisking well to avoid lumps. Leave the batter to rest at room temperature for 30 minutes. Or, for even better results, refrigerate for 24 hours then leave to come to room temperature for 30 minutes before using.
Preheat the oven to 230C. Put 1 teaspoon of beef drippings into each off the cavities in the muffin tin. and heat in the oven until smoking hot.
Working quickly, fill each muffin cavity 3/4 full of batter and return the pan to the oven. Bake for 15-20 minutes until well risen and firm. Serve immediately - or cool and freeze, then reheat in a hot oven next time you cook a roast.