In a large bowl, cream butter and sugar until light and fluffy, 5-7 minutes. Beat in eggs and vanilla. In another bowl, whisk flour, cocoa, baking soda and salt; gradually beat into creamed mixture. Refrigerate, covered, 1 hour or until firm enough to shape., Preheat oven to 350°. Shape level tablespoons of dough into balls; place 2 in. apart on ungreased baking sheets. Bake until cookies are set, 6-8 minutes. Using a 1-1/4-in. heart-shaped cookie cutter, score the center of half of the cookies. Cool completely on pans on wire racks., Using the same heart-shaped cookie cutter, gently cut scored cookie tops and remove the center of each. Spread marshmallow creme over the bottom of the solid cookies; cover with remaining cookies., Freeze option: Freeze shaped balls of dough on baking sheets until firm. Transfer to airtight freezer containers; return to freezer. To use, bake cookies as directed.