Preheat the oven to 220ºC/gas mark 7. Add 2 tsp oil to each of 4 x 18½cm sandwich cake tins and put them in the oven to heat up.
Meanwhile, sift the flour into a large bowl and make a well in the centre. Beat in the eggs until smooth, then gradually add the milk, beating until the mixture is smooth and free of lumps.
Pour the batter into a jug. Remove the hot cake tins from the oven and carefully pour a quarter of the batter into each tin. Bake for 20 minutes, or until the puddings are well risen and golden in colour.
Fill the Yorkshires with your roast dinner and gravy, and serve immediately.