Heat oven to 325 degrees F. Coat a 9-inch springform pan with nonstick cooking spray.
In a medium-size saucepan, heat 1-1/4 cups of the apple juice concentrate with the prunes and butter over medium heat. Cook until butter is melted and mixture just begins to simmer, about 6 minutes. Remove from heat and let stand 5 minutes.
Meanwhile, whisk together flour, 3/4 cup cocoa, baking powder, baking soda and salt in a large bowl. Carefully transfer apple juice mixture to a blender and mix until prunes are pureed.
Beat eggs in a large bowl until blended. With mixer on medium speed, slowly add apple juice mixture. Beat until evenly blended. On low speed, beat in half the flour mixture, then milk, then remaining flour mixture. Stir in vanilla; spread into prepared pan. Bake at 325 degrees F for 50 minutes or until toothpick inserted in center of cake comes out with moist crumbs. Cool in pan on wire rack 10 minutes; then remove pan and cool completely.
Meanwhile, combine raspberries, remaining apple juice concentrate and 2 tablespoons water in a mini chopper. Pulse until pureed. Strain through a sieve; discard solids. Once cake has cooled, dust top with a little cocoa powder. Slice and serve with raspberry puree and sugar-free ice cream.