PREHEAT oven to 325° F. Grease 13 x 9-inch baking pan.
COMBINE flour and baking soda in small bowl. Beat ½ cup brown sugar, granulated sugar and butter in large mixer bowl until creamy. Beat in egg yolks and vanilla extract. Gradually beat in flour mixture until crumbly. Stir in 1½ cups morsels and ½ cup nuts. Press dough onto bottom of prepared baking pan.
BEAT egg whites in small mixer bowl until soft peaks form. Gradually beat in remaining brown sugar until stiff peaks form; spread over dough. Sprinkle with remaining morsels and remaining nuts.
BAKE for 35 to 40 minutes or until top is set and lightly browned. Cool in pan on wire rack for 20 minutes. Cut into bars while still warm.