I have made Yorkshire pudding two times. First time was with butter, which burned, and second time with olive oil which turned out better. But the problem is that whenever I make them, they are always under-done. I usually cook it for 15-20 minutes. Am I doing something wrong?
We are not sure whether you are making one large yorkshire pudding or smaller individual ones in a yorkshire pudding tin or a muffin tin but we would suggest that ideally the cooking vessel should be made of metal. The tin needs to be preheated, along with the cooking fat, and metal is ideal as it preheats quickly and also will conduct the heat of the oven more readily when cooking the yorkshire pudding. 15-20 minutes should be enough time for smaller Yorkshire puddings but for larger ones you will need to increase the cooking time slightly to make sure that the pudding does not have a soggy centre. The size of your tin is also important as the uncooked batter should come around 1/3 up the sides of the pan (ie the pan should be about 1/3 full, whether it is one large pudding or smaller ones) so if your batter is filling up the pan more than this maybe try using a larger tin or reducing the quantity of batter accordingly.
We would also suggest changing the type of fat used for cooking.Yorkshire puddings are cooked at a very high oven temperature. Butter is unsuitable as it burns very easily but olive oil also has a relatively low "smoke" point and so is not the ideal choice. Instead choose a fat with a high smoke point such as vegetable or sunflower oil, lard or solid vegetable shortening (eg Flora White, Trex, Crisco). If you like the flavour from the olive oil then add a little to one of the cooking fats mentioned above. Using one of the fats above will reduce the risk of the oil on the outside burning before the inside of the pudding has cooked. Let the tin and fat heat in the oven for at least 5 minutes, you want to fat to sizzle slightly when the batter is added to the tin.
If the batter in the centre still remains under cooked then you may need to reduce the oven temperature by 20-40c (50-75F) after the initial cooking and give the pudding an extra 5 minutes in the lower oven at the end to cook through. If you are making smaller individual puddings then you can also ease them out of the indentations/cups in their tin, turn them upside down (so they are sitting upside down over the indentations in the tin) and give them another 3-5 minutes in the oven to cook through - the bases are more exposed to the direct heat of the oven and this can help them to cook through more readily.