1. Preheat oven to 325°F. Line an 8-inch square baking pan with foil or parchment so that 2 sides overhang; mist lining with cooking spray.
2. Combine prunes, coffee, milk, oil, eggs and vanilla in a food processor; process until smooth. In a large bowl, combine sugar, cocoa, flour and salt; mix well. Stir prune mixture into flour mixture until well combined. Stir in chopped chocolate. Spread evenly in baking pan.
3. Bake until set, about 20 minutes. Let cool in pan on a wire rack.