COMBINE flour, cocoa, baking powder, baking soda and salt in small bowl. Beat butter, sugar and vanilla extract in large mixer bowl until well blended. Add eggs; beat well. Gradually beat in flour mixture. If dough is slightly crumbly and does not hold together, add 1 to 2 tablespoons of water. Shape dough into ball. Divide dough in half and place each on plastic wrap. Flatten each into an 8-inch circle. Wrap and refrigerate for 30 minutes.
PREHEAT oven to 350° F.
ROLL out one circle of dough on lightly floured surface to 1/8-inch thickness. Cut out hearts with larger cookie cutter. Transfer to ungreased baking sheet(s), placing about 2 inches apart. For sandwich cookies, use smaller cutter to cut out hearts in centers of the larger hearts on the baking sheet. Lift smaller center heart with tip of knife; place on baking sheet near the larger hearts. Repeat with trimmings and other circle of dough.
BAKE for 5 to 6 minutes or until tops are set. Cool on baking sheets for 2 minutes; remove to wire racks to cool completely.
DIVIDE vanilla frosting in half. Tint half pink with red food coloring. Frost hearts and top with other hearts for a sandwich. Decorate as desired. Store in single layers between sheets of wax paper in tightly covered container.