Pre-heat the oven to 230°C. Prepare the Yorkshire pudding batter by sifting the flour into a bowl with some seasoning, then whisk the egg in until incorporated.
Whisk in milk and water until you have a smooth batter. Strain into a jug and set to one side. Divide the sunflower oil evenly between a 4-hole Yorkshire pudding pan.
Heat the oil in the oven for 10 minutes until smoking hot then remove and carefully pour the Yorkshire pudding batter into the oil, filling it up to the top of the moulds.
Return to the oven and bake for 8-10 minutes until golden, risen and crispy. Remove and serve immediately.