Mix together the milk, eggs, flour and a pinch of salt in a food processor or blender until you have a smooth batter. If you don’t have a food processor or blender, whisk the eggs into the flour and salt, then gradually whisk in the milk until smooth. Transfer to a jug, cover and leave for 15 mins.
Meanwhile, heat oven to 240C/220C fan/gas 9. Pour ½ tsp oil into the holes of a Yorkshire pudding or muffin tin and put in the oven for 10 mins to get hot.
When the oil is hot, pour the batter into each hole a third of the way up. Quickly put in the oven, then turn it down to 180C/160C fan/gas 4 and cook for 12-15 mins. Remove the Yorkies, turn them upside down in the tin and return to the oven for another 2-3 mins to brown the bottoms.
Allow to cool completely on a wire rack, then put in a tight-sealing freezer bag or container and freeze for up to a month.
When ready to cook, heat oven to 220C/200C fan/gas 7. Put the frozen Yorkies on a baking sheet and cook for 6-8 mins until golden and hot.