Rinse the tongue and place it in a large stockpot. Add enough water to cover - I use 14 cups of water.
Bring to a boil. This will likely take 20-30 minutes. Skim the foam off from the top.
Lower the heat to a simmer. Add the bay leaves, peppercorns and allspice, and cook, partially covered, turning the tongue every hour to ensure even cooking on all sides. Cook 3 hours for a 2-lb. tongue, 4 hours for a 3-lb. tongue.
Remove the cooked beef tongue to a cutting board. Allow it to cool until easier to handle, then remove the skin, as shown in the video, slice and serve, with or without sauce.
To make the sauce, heat a large, deep skillet over medium heat. Add the butter and swirl to coat. Add the onions and cook, stirring occasionally, until caramelized, 10 minutes.
Add the mushrooms and cook, stirring, until soft.
Add broth, salt and pepper. Bring to a boil over high heat. Add the sliced tongue, cover it with the sauce, lower heat to a simmer, and cook, uncovered, for about 30 minutes.
If you wish to thicken the sauce, 5 minutes before it’s done, mix 1 teaspoon cornstarch with 2 teaspoons of cold water and stir the mixture into the sauce.
1. Nutrition info assumes a 2-lb. tongue.2. You can simply cook the sauce separately as I do in the video and then spoon it on top of the cooked tongue slices. In that case, use 1 onion, 8 oz mushrooms, 2 TBS butter and just 1 cup of broth.3. You can use the tongue cooking water as a very tasty broth. I don’t add any salt to the cooking water to ensure the meat remains as tender as possible. If not using the sauce, you can sprinkle the cooked tongue slices with some salt. You can also mix salt into the broth after removing the tongue.