COMBINE flour and baking soda in medium bowl.
MICROWAVE morsels and butter in large, uncovered, microwave-safe bowl on MEDIUM-HIGH (70%) power for 1 minute; STIR. The morsels may retain some of their original shape. If necessary, microwave at additional 10 to 15-second intervals, stirring just until morsels are melted. Beat in sugar, eggs and vanilla extract. Gradually beat in flour mixture; stir in nuts. Cover; refrigerate for about 1 hour or until firm. Shape into two 14 x 1 1/2-inch logs; wrap in plastic wrap. Refrigerate for 2 hours or until firm.
PREHEAT oven to 375° F.
UNWRAP logs; slice into 1/4-inch-thick slices. Place slices on ungreased baking sheets. Bake for 5 to 6 minutes or until edges are set. Cool on baking sheets for 2 minutes; remove to wire racks to cool completely.