This is the classic companion dish to roast beef. To start with, it's not a pudding, at least, not what most Americans think of as a pudding. As George Bernard Shaw commented, Great Britain and the USA are two countries kept apart by a language held in common. Life goes on.
More important than what Yorkshire Pudding is not is what it is. It's a great substitute for potatoes, rice, or other starches. It's crisp on the outside, fluffy on the inside, and very tasty.
You should prepare this the next time you have roast beef, or London Broil, or just about anything. It's that good.
Well... let's get on with baking a yorkie. (Some people don't like that term for a Yorkshire pudding, since "yorkie" is a slang term for small obnoxious dog, the Yorkshire Terror, but that's another story.) This is a quick recipe from "James Beard's American Cookery".
1 c milk
1 c sifted all-purpose flour
1/2 tsp salt
1/2 tsp freshly ground black pepper
Start by pre-heating the oven to 450F. Beat the eggs until quite light and gradually beat in the milk and sifted flour. (Or put all in a blender or mixer and beat or spin until batter is smooth). Season with salt and pepper and a tablespoon or two of hot drippings if you like. Heat an 11 x 14 pan and pour in a heavy layer of hot beef drippings. Pour in the batter and bake at 450 F about 10 minutes then reduce the heat to 375 and continue baking until golden brown, about 15 to 20 minutes. NOTE: Do NOT open the oven door during the first 20 minutes of baking. You can also use muffin pans to make individual servings.
To serve the large pan, just cut the pudding into squares and take the baking dish to the table.
Some comments about the beef drippings
You may be wondering why the beef drippings are added at all. Originally, Yorkshire Pudding was baked under a roast of beef. In those days, beef was roasted at high temperatures for a fairly short time. So, there were lots of drippings. And they flavored the pudding. Today, we cook at lower temperatures for longer periods. And what drippings there are, are spread out over a much longer period of time. By the time you're ready to bake the pudding, there aren't many drippings left. So, catch the drippings in a pan and then put them onto the pudding. In a pinch, thickened beef broth can be used, as can butter, or you can omit the drippings altogether.
If you are serving vegetarians, you may omit the beef drippings, or (perhaps) substitute a mixture of vegetable oil and vegetable broth. (That sentence sounds odd, and I need to work on it. And "if you're having vegetarians for dinner" isn't any better. How about, "if you are entertaining vegetarians"?)