Don't have the exact details to hand but:
Get one of those yorkshire pudding tins with the four indents. Put splash of oil or knob of dripping or lard, (whatever you prefer) in each dent, and put in oven to heat up.
Make largish (bit bigger than golf ball?) meatballs out of minced beef (or I suppose lamb) and finely chopped onion. (mix mince and onion and seasoning, and shape into balls, using flour covered hands to prevent sticking. No need to bind with egg or anything.
Place one ball in each indent of tin, and put in oven for 5 minutes.
Meanwhile, make Yorkshire pudding batter (look up recipe...). After 5 mins precooking, take tin out, and pour batter around each meatball. Put back in oven and bake until pudding is cooked - about 15 mins. (look up the temp for yorkshire pudding, I can't remember off hand)
Serve with choice of potatoes and veg, and gravy. Goes well with a dark green veg like kale or brocolli.
Sorry, amounts are a bit vague, I don't have the book to hand. It'll be either 8 or 4 ounces of mince, for 4 popovers.