Step 1 – Place the tongue, vinegar, onion, salt, pepper corns, cloves, bay leaves and parsley in a large pot. Add enough water to cover the ingredients. Cook on medium heat. After 45 minutes, reduce the heat and continue to cook covered for 2 hours or until the tongue is very tender, then remove from heat. Let tongue cool in the broth, uncovered.
Step 2 – For the walnut sauce: Place breadcrumbs in a bowl and pour 2 cups of the tongue broth over it. Soak for a few minutes. Place the bread and soaking broth in a pot and cook on a medium heat, stirring until the mixture thickens slightly.
Step 3 – Heat the oil in a pan over a medium heat and fry the onion until it is lightly browned. Add the walnuts, wine, salt and pepper. Pour the mixture into the pot with the bread sauce and cook on medium heat, stirring. Finally, add the cream and cook for a few minutes over medium heat, stirring constantly.
Step 4 – Remove the skin from the tongue and cut the tongue into medium strips. Place the strips in a bowl or individual plates and pour the hot walnut sauce over them. Serve immediately.