Brush a 6-cup loaf pan with melted butter. Let cool. Line pan with waxed paper or parchment paper and set aside to soften. In a small bowl soak the prunes in the Armagnac, Cognac, or boiling water. Melt the chocolate and butter together in the top of a large double boiler set over simmering water, stirring often. Turn off the heat and let cool slightly. Whisk in the cold egg yolks, then set the mixture aside in the double boiler. Do not turn on the heat. The mixture will stay warm over the hot water. Whip the cold egg whites in a mixer fitted with a whisk attachment (or using a hand mixture) until they form soft droopy peaks. With the mixer running, slowly add the granulated sugar and whip until stiff and glossy, about 30 seconds. Fold the egg whites into the warm chocolate mixture until barely blended. Fold in the prunes (with any liquid that has collected in the bowl) until no streaks of egg white remain. Pour into the pan and cover tightly with plastic wrap. Chill at least 2 hours or overnight. When ready to serve, whip the cream and brown sugar together until soft peaks form. Unmold the pave onto a serving platter and peel off the paper. Serve in slices, topped with whipped cream.
Recipe courtesy of Gale Gand, ¿Butter Flour Sugar Eggs¿