Vitello is veal, very difficult to find in the US. I use pork loin with great results.
Insert the thermometer deep inside the meat.
In a large pot place meat, wine, onions, carrots, celery, bay leaves, and pepper corns. Add enough water to cover the meat. Simmer at low heat until the internal temperature of the meat reaches 150 degrees.
Transfer the meat to a platter and let it cool. Strain and reserve the cooking broth.
Refrigerate the meat for at least 24 hours.
To make the sauce:
Combine tuna, anchovy, capers, and lemon juice in a blender and blend to a very smooth mixture. Add mayonnaise and 1 T of cooking broth (add more if desired a thinner consistency). Refrigerate in a tightly sealed container for at least 2 hours.
Thinly slice the meat and arrange on a platter. Drizzle the sauce over each slice. Garnish with additional capers.
If you can, make mayonnaise from scratch using egg yolks, good olive oil, lemon juice, salt and pepper.