In large bowl with mixer at medium speed, beat margarine, sugar, melted chocolate and egg until creamy. Stir in buttermilk and vanilla until smooth. Mix in flour, baking soda and salt until blended; stir in holes and walnuts. Cover and chill dough at least 1 hour. Drop dough by level tablespoonfuls, 2" apart, onto ungreased baking sheets. Bake at 400'F. for 8-10 minutes or until set. Remove from sheets, cool on wire racks. Makes 3 dozen cookies.