PREPARATION:

1. Place chocolate in 1-cup glass measuring cup. Microwave, uncovered, at HIGH 1 to 1-1/2 minutes or until chocolate is melted, stirring after 1 minute; set aside.
2. Beat butter and sugar in large bowl until light and fluffy. Beat in egg and vanilla. Gradually beat in chocolate. Combine flour, baking soda and salt in small bowl; add to butter mixture. Form dough into two discs; wrap in plastic wrap and refrigerate until firm, at least 2 hours. (Dough may be refrigerated up to 3 days before baking.)
3. Preheat oven to 350°F. Grease cookie sheets. Roll one dough disc between two sheets of waxed paper to 1/4- to 1/8-inch thickness. Remove top sheet of waxed paper; invert dough onto prepared cookie sheet. Score dough into 3X2-inch rectangles. Do not cut completely through dough. Cut excess scraps of dough from edges; add to second disc of dough and repeat rolling and scoring until all of dough is scored. Pierce each rectangle with fork.
4. Bake 10 minutes or until set. Let cookies stand on cookie sheets 1 minute. Cut through score marks while cookies are still warm. Remove cookies to wire racks; cool completely. Spread half of cookies with softened ice cream; top with remaining cookies. Wrap in plastic wrap and freeze 1 hour or up to 2 days.