Four inches is the official height for a Yorkshire Pudding.
The Royal Society of Chemistry suggested in 2008 that a “A Yorkshire Pudding isn’t a Yorkshire Pudding if it is less than four inches tall”
Originally the Yorkshire Pudding was served as a first course. The dripping fat from the roasted meats created a rich gravy and was poured over the low-cost starter made from flour, eggs and milk similar to a good pancake batter.
The batter was put into an extremely hot iron pan with a bit of butter to fry the bottom of the pudding over a hot open fire,. Then it was placed under a shoulder of mutton. The fat that dropped into the dripping pan cooked the battered and became a light and savory first course with the rich gravy poured over the pudding.
The “dripping pudding” (later named “The Yorkshire Pudding”) became popular in the north of England when flour became a common use for making cakes and in 1737 a recipe for Yorkshire pudding was published in the book “the Whole Duty of a Women”