1In large bowl, beat butter and sugar with electric mixer on medium speed 30 seconds or until smooth. Add 1/2 cup of the walnuts and the egg yolk; beat until blended. On low speed, beat in flour, baking powder, salt and maple flavor until stiff dough forms. Shape dough into a ball. Wrap in plastic wrap; refrigerate 45 minutes.
2Heat oven to 350°F. Divide dough into 8 equal parts. On lightly floured surface, shape each part into a rope 12 inches long and 3/4 inch thick. Cut into 2-inch lengths. On ungreased cookie sheets, place cookies about 2 inches apart; flatten slightly.
3Bake 15 to 17 minutes or until edges begin to brown. Cool 2 minutes; remove from cookie sheets to cooling racks. Cool completely.
4In small microwavable bowl, microwave chocolate chips uncovered on High 1 minute 30 seconds, stirring every 30 seconds, until chips can be stirred smooth. In another small bowl, place remaining 1 cup walnuts. Dip 1/2 inch of 1 long side of each cookie into chocolate, then coat chocolate edge with walnuts. Place on waxed paper; let stand about 2 hours until chocolate is set.