One hour before roast is finished, prepare Yorkshire pudding batter. Place eggs in a large bowl; whisk in milk, then flour (one cup at a time), then salt and pepper. Continue whisking until almost no lumps remain. Let mixture sit at room temperature.
When roast is done, turn oven up to 450 F and return pan with drippings to oven for 5 minutes, or until the fat starts to bubble. Take pan out, pour batter in and return it to oven. Cook 30 minutes.
Reduce temperature to 350 F, continue cooking for 10 more minutes. Bring directly to the table-quickly, before it deflates in the pan.