According to the BBC, Yorkshire pudding was used originally as a first course filler for people who couldn't afford much meat. Later, when roasts were cooked on a spit, the batter was put underneath so the drippings could fall into the batter. Now the dish is almost always served with a roast beef as a "traditional English dinner." The American version is the popover which is very similar but most often is served with jam or honey as opposed to the English habit of pouring gravy over them.
My mother would usually make hers in a baking pan and it would come out as one big, puffy, glorious pudding which would be cut into individual segments at the table. It was high drama when the pudding was ready and it would wait for no one, so everyone had to be ready for the big event of it coming to the table. I have found the individual muffin tins to be best in my home as we inevitably have leftovers and they are easy to save for the next day in this format.
Yorkshire Pudding is another one of my family's traditional English dishes that I am so happy I know how to make.
1 cup all purpose flour
1/2 tsp salt
2 large eggs
1 1/4 cups whole milk
4 Tbsp fat (beef drippings, melted butter or vegetable oil)
Preheat oven to 425 degrees. Put the flour and salt in a bowl. Add the eggs and milk and beat until well mixed and smooth. The batter should be the consistency of heavy cream. If needed, add more milk. Cover the batter and let stand at room temperature for 30 minutes.
Put 1 tsp of fat in each of the muffin tins and put the tin in the oven. When the fat is very hot, portion the batter evenly among the cups; the batter should sizzle in the hot fat. Return the tin to the oven and bake for 20-25 minutes. The puddings are done when they are puffed, browned and crisp. Serve immediately with roast beef, roasted vegetables and gravy. (Note: these are almost as good the second day if you heat them in the toaster oven at 250-300 degrees for fifteen minutes or so.)