Guinness braised beef with fluffy mashed potatoes is the ultimate St. Patrick's Day meal. A beef roast is cooked low and slow with onions, carrots , sherry and Guinness beer. The secret ingredient to this recipe (besides the Guinness) is the tablespoon of cocoa powder which adds richness and depth of flavor to the meat. After 6-8 hours, your beef roast will be absolutely tender and delicious. When you are about to serve, pile on the Guinness braised beef over a bed of mashed potatoes and reserve plenty of the cooking liquid for a sauce.