Add oil in the muffin baking tins, and preheat the oil for about 10 minutes (in the preheated oven). Once the oil is preheated, take it out and pour batter in. (Use a measuring cup for easier pouring into the muffin cups and try not to splatter). Do not fill the muffin cups to the top.
Some will go down when the cool air hits just baked Yorkshire Pudding. It is normal, but some might stay nice and crispy. I filled several with pudding and whipped cream, but you can use whatever filling that you like if you wish to serve it as a dessert.