Thaw pastry sheet at room temperature for 30 minutes. Preheat oven to 400 degrees.
Unfold pastry on lightly floured surface. Roll into 10-by-14-inch rectangle. Cut a piece of paper into a heart 7 inches long by 7 1/2 inches wide; use as a pattern to cut out 2 hearts. Cut 6 small hearts out of remaining dough. Place hearts on baking sheet. Sprinkle hearts with 2 tablespoons of the granulated sugar. Bake 15 minutes or until puffed and golden; cool on a wire rack.
(For a decorative touch: Before baking the pastry, with the tip of a small, sharp knife, crosshatch one of the large hearts to form 1/2-inch diamonds; small hearts can also be crosshatched.)
In a large bowl, with mixer at high speed, beat cream, confectioners' sugar, cocoa and liqueur until soft peaks form. Spread mixture over the undecorated heart, leaving a 1/2-inch border.
Arrange 1/3 cup of the raspberries over cocoa filling. Top with remaining heart, sugar side up. Place tart on a serving plate. In a blender container, place remaining 2/3 cup raspberries and remaining 1 tablespoon granulated sugar; blend until smooth. Spoon sauce around edge of plate; garnish plate with small hearts. Makes 2 to 4 servings.