PREPARATION:
- Place 1 oven rack in the top third of oven and 1 oven rack in the bottom third of oven; preheat oven to 300°F. Line 2 large cookie sheets with aluminum foil, shiny side up.
- Stir powdered sugar and 1/2 cup walnuts with fork in medium bowl; set aside. Crumble brown sugar into small bowl; set aside.
- Beat egg whites and salt in large bowl with electric mixer at high speed until foamy. Add cream of tartar; beat 30 seconds or until mixture forms soft peaks. Sprinkle brown sugar, 1 tablespoon at a time, over egg white mixture; beat at high speed until each addition is completely absorbed. Beat 2 to 3 minutes or until mixture forms stiff peaks. Beat in maple extract at low speed. Gently fold in walnut mixture.
- Drop level tablespoonfuls of dough to form mounds about 1 inch apart on prepared cookie sheets. Sprinkle cookies with remaining 1/3 cup ground walnuts. Bake 25 minutes or until cookies feel dry on surface but remain soft inside. (Rotate cookie sheets from top to bottom halfway through baking time.)
- Slide foil with cookies onto wire racks; cool completely. Carefully remove cookies from foil. Store in airtight container with waxed paper between layers of cookies. Cookies are best the day they are baked.
