Prepare the Ingredients: Begin by slicing the liver, chopping the bacon or pancetta, slicing the onions, crushing the garlic, and cutting the mushrooms into bite-size pieces. Set aside.
Brown the Liver: Lightly coat the sliced liver in flour seasoned with salt and pepper. Heat a large pan over medium heat and brown the liver slices in batches. Once browned, remove the liver from the pan and set aside.
Cook the Bacon and Vegetables: In the same pan, add the bacon or pancetta, cooking until it starts to crisp. Then, add the sliced onions and garlic, cooking until the onions are soft and translucent. Add the mushrooms and cook for a further 5 minutes.
Combine and Simmer: Return the liver to the pan with the bacon and vegetables. Stir in the tomato puree and then slowly add the beef stock, ensuring the mixture is well combined. Bring to a simmer, cover, and let cook gently for about 1 hour, or until the liver is tender and the sauce has thickened.
Final Seasoning: Taste and adjust the seasoning with salt and pepper as needed. Serve hot, ideally with a side of crusty bread or creamy mashed potatoes.
