Make Filling: In a 3 quart saucepan, place prunes and 2 cups water; heat to boiling. Reduce heat, and simmer, covered, 30 minutes, or until prunes are very tender.
Drain prunes, reserving liquid. Chop prunes finely. Add 3/4 cup granulated sugar, 1 teaspoon vanilla; the cardamom, 1/4 teaspoon salt, and 1/2 cup reserved cooking liquid; mix until ingredients are well blended. Set aside to cool.
Make torte layers: Sift flour with baking powder and salt. In a large bowl, with electric mixer at high speed, beat butter with granulated sugar and vanilla until light and fluffy. Add eggs, one at a time, beating well after each addition. At low speed, add flour mixture alternately with milk, beginning and ending with flour mixture. Refrigerate dough until chilled and easy to handle-about 20 minutes. Preheat oven to 350 degrees. Divide dough into 7 equal pieces. For each layer, invert an 8-inch round layer cake pan. Flatten a piece of dough with hands; place on pan; pat to fit. Then gently roll to make layer even; trim edge if necessary. Keep pieces of dough refrigerated until ready to use. Bake 15 to 20 minutes, or until edge is golden brown. Carefully remove to wire rack; let cool. To assemble: Place one layer on serving plate; spread with about 1/2 cup filling. Repeat with 5 more layers and remaining filling. Set last layer on top. Cover completely with plastic film or foil. Refrigerate at least 24 hours, to mellow. To serve: Sprinkle top with confectioners sugar. Cut in thin slices. Pass whipped cream. Return unused portion to refrigerator.