Traditionally you eat Yorkshire pudding with roast beef but I love it with any roast. It is best if you let the batter sit for an hour before cooking but when I forget it still works out fine.
Preheat the oven to as hot as you can get it. Place 1 tablespoon of fat in a cake tin and place it in the oven to get very hot 5 minutes before you plan to start cooking.
Beat together the self raising flour, salt, egg and enough milk to create a smooth runny batter. Let sit for 1 hour.
Pour the batter into the hot preheated cake tin then return to the oven and cook for 20 minutes.