Soften gelatin in water in a heat-proof dish, 3 minutes. Place dish in a skillet of simmering water; stir gelatin to dissolve Slice cake into scant 1/2 inch thick slices. fit slices in bottom of a 13 X 9 X 2-inch baking pan in single layer, cutting and adding scraps to fit snugly. Drizzle liqueur over cake. Process cream cheese, ricotta, sugar and cocoa in food processor until smooth. Add gelatin mixture, processing to blend. Add chocolate pieces, processing just to combine. Scrape into prepared pan, spreading over cake. Cover with plastic wrap. Chill 3 hours, or until set. Dust with cocoa and cut into squares.