Dice the onion (one onion), slice the mushrooms (300g) and slice four of the pickled walnuts.
Add half the olive oil (½ tbsp) to a large saucepan. Heat and then add the diced beef (800g). Cook until the beef has browned, stirring regularly to ensure it cooks evenly. Once the beef has browned, remove it from the pan and set aside.
Add the remaining olive oil (½ tbsp) to the pan. Heat and then add the chopped onion. Reduce the heat to low and cook the onion for 4-5 minutes until it starts to soften and brown, stirring regularly.
Return the beef to the pan. Add the flour (1 tbsp) and stir to coat the beef in the flour. Add the chopped mushrooms, pickled walnuts, ruby port (200ml) and stock cube (crumbled). Top up the pan with water until the level of the water just reaches the top of the other ingredients. Bring to the boil, then reduce the heat to a simmer. Cover and simmer for 1½ hours, stirring occasionally.