Preheat oven to 350°F. Butter a 10-inch springform pan and dust with cocoa powder, knocking out excess.
In a skillet cook prunes, Armagnac, and gingerroot over moderately high heat, stirring frequently, until almost all liquid is evaporated. Remove pan from heat.
Into a bowl sift flour, baking soda, spices, and salt. In another bowl with an electric mixer cream shortening. Add sugar, beating, and beat mixture until light and fluffy. Add molasses in a stream, beating until combined well. Beat in coffee, flour mixture, eggs, and vanilla until batter is just combined. (It may separate at this point.) Reserve 1 tablespoon crystallized ginger and stir remainder into batter with prune mixture. Turn batter into prepared pan and sprinkle top with reserved ginger.
Bake gingerbread 1 hour 20 minutes, or until a tester comes out clean, and cool on a rack 1 hour. (The gingerbread will fall slightly in center.)
Serve gingerbread warm or at room temperature with crème fraîche and kumquats.
