Warm the cream in a saucepan over low heat until it approaches a simmer. Add the Parmigiano, stirring constantly to melt it completely.
Remove the cream and cheese mixture from the heat and add 1 teaspoon of the vinegar and a few generous grindings of pepper.
Place the mortadella pieces into a food processor and pulse until finely chopped. With the motor on add the cream mixture in a slow steady stream until all cream has been taken in.
Taste for seasoning and pour into 6 or 8 individual dishes -- the white-fluted souffle type or any "pudding" dish. Cover tightly with plastic and refrigerate for several hours to set.
Meanwhile, build the sauce. In a medium saucepan, reduce the red wine by half its volume; lower the flame and add the cherries, gently simmering together for 5 minutes. Add the butter and simmer for another minute.
Off the heat, add the remaining tablespoon of vinegar and the walnut liqueur, stirring well to blend. Set aside.
Remove the mousse from the refrigerator 1/2 hour before serving. Place the individual dishes on large, flat plates. Place some walnut halves and a few pieces of toast on each plate and drizzle the warm cherry sauce over the mousse.
At the table, a little of the mousse and its sauce is spread on toast and topped with a piece of walnut.