As we said above, Vitello Tonnato is a traditional recipe, which has been changed and modified throughout the decades. If the cooking method for the veal remains very much the same, differences are easily encountered when it comes to the sauce. The most common alternative to the traditional sauce, which is made with a base of boiled egg yolks, is that made with mayonnaise instead.
Here is a basic recipe for it:
In a mixer, blend together the tuna, the capers and the anchovies. If the mixture is too dry, you can add a tablespoon or two of the veal's cooking broth. Once it is smooth, add 250 gr of mayonnaise and mix well with a spoon. Voilà: your mayo based salsa tonnata is ready.
Ideally, you should prepare the mayonnaise yourself, as nothing tastes as good as homemade mayo! In alternative, make sure to pick high quality mayonnaise from the store, as a bad mayo could ruin the final result!