Prepare the pate: Line a 9 by 5-inch loaf pan with parchment paper or foil; set aside. Melt the chocolate in a double boiler over low heat. Add the wine and whisk to blend. Remove from the heat and stir in the nuts. Cool to room temperature.
Whip the cream until soft peaks form. Gently fold the chocolate mixture into the whipped cream.
Pour into lined loaf pan, cover, and refrigerate overnight or at least 3 hours. (The pate can be made up to 5 days in advance.)
Prepare the sauce: Melt the butter in a saute pan over medium heat. Add the plums and saute until the plums begin to soften, 2 to 3 minutes. Add the sugar and cook until the sugar begins to caramelize, 4 to 5 minutes. Add the wine and simmer over low heat until slightly thickened, 3 to 5 minutes. Remove from the heat and stir in the nutmeg. (The sauce can be prepared and refrigerated up to 24 hours in advance. Serve at room temperature.)
Prepare the topping: Whip the cream until soft peaks form. Sprinkle in the sugar and vanilla and whip just to blend.
To serve: Use a warm knife to slice the pate into 1/2-inch slices. Top each serving with plum sauce and whipped cream.