Cut the steak into bite sized pieces and place into a bowl. Add the peppercorns and bay leaves and pour over the Guinness® and cover. Leave in the fridge overnight to let the flavours absorb (if you don’t have time you can skip this step but it’s way better if you do it).
Finely slice the onion, garlic and celery. Chop the carrots and mushrooms into bite sized pieces. Fry all of these in the cooking oil, in a large saucepan, on a medium heat.
When the vegetables are softened, spoon the steak out of the Guinness® and into the pan. Allow the beef to brown on all sides and then add the flour. Stir and let it cook for about 2 minutes, then pour in the Guinness® from the marinade and the stock.
Bring this to the boil and then reduce to the lowest heat. Add the Worcestershire sauce, tomato purée and salt. Cover, and allow to simmer for as long as you possibly can, checking on it every 20 minutes or so to make sure nothing’s sticking. I cooked mine for about 90 minutes and it was perfect.
Serve with your mashed potatoes (or in my case, on this occasion, cauliflower mash) or crusty bread. Don’t worry about leftovers, they’ll be even more delicious the next day.