Preheat the oven to gas 7, 220℃, fan 200℃. Pour 2 teaspoons of rapeseed or sunflower oil into each hole of 2 x 6-hole muffin tins (or a 12-hole muffin tin). Put in the oven for 15 mins.
While the tins are heating up, crack 2 eggs into a large bowl. Measure 225ml (7 1/2fl oz) semi-skimmed milk into a jug. Beat the eggs well with a balloon whisk.
Mix 1/4 teaspoon of salt with 115g (3 3/4oz) plain flour then add to the bowl 2 spoonfuls at a time, adding 2 tablespoons of the milk with the final batch of flour. Whisk until smooth and thick.
Slowly start to pour the rest of the milk into the mixture, just a little at a time at first, beating well as you go, to make a smooth batter. Transfer the batter to a jug.
When the fat in the tins (or tin) is very hot, carefully remove from the oven and pour in the batter to half-fill each hole. The fat should sizzle as you pour the batter in.
Bake for 15-20 minutes until the Yorkshire puddings are well risen, golden (don't open the oven door mid-cooking). Serve them as quickly as you can, while they are still tall and puffy.