Cover the bottom of each section with oil. Place the mini muffin tin on a cookie sheet on the middle rack of a pre-heated oven and heat the oil almost to the smoking point, about 3-4 minutes.
In the meantime, combine flour, milk, eggs and salt in a bowl and mix with a wire whisk until the batter is smooth and a little looser than pancake batter.
When the oil has become hot, pour the batter into each of the 12 muffin sections to nearly the top.
Bake for 20-30 minutes or until the Yorkshire Puddings are puffed and golden brown.
A friend living in the UK recently reminded me that flour can make all the difference in the world when making Yorkies. This is after I complained that a recipe from a British chef seemed to be too thick and the Yorkshire Puddings seemed very eggy and doughy. At the moment I am in the US and I find that flour here is somehow denser than in Canada so I have modified this recipe to take that into account. But I think that the best approach is to judge the batter by it's density. I like a batter that is thin, more like crepe batter or a thin pancake batter. So this means use less flour, or thin out the batter with milk or water until you get the desired consistency. A bit of trial and error.