Yorkshire Pudding Help

becs

My hubby does amazing yorkies that are the envy of all, everyone always asks him to make them for any ocassion. He's also going to be doing a cookery course to show people how to make them as part of a local "greeniversity" thing. His recipe and method is for 12 in muffin tin:
5oz plain flour
3 eggs
1/2 pint of milk
Appx 50ml of water
Mix by hand but not overwhisk as any lumps will cook out, he usually uses normal vegetable or sunflower oil appx teaspoon in the bottom of each cup, heat in an oven at 200 for 10 mins. Pour in the batter then cook for appx 15 mins then turn down to 160 for another 15-20 mins. These are fan oven temps and another for don't open the door! The initial high heat makes them rise then the second part of the cooking cooks them through without overdoing them so they stay nice and tall. His usually are a minimum of 3" ABOVE the tin!