In a large bowl, beat butter and sugars until blended. Beat in eggs and vanilla. In a small bowl whisk flour, baking soda and salt: gradually beat into butter mixture, Stir in chocolate chips and walnuts.
Shape 1/4 cupful of dough into balls. Flatten each to 3/4" thickness (2 1/2" diameter) smoothing edges as necessary. Place In an airtight container, separating layers with waxed paper or parchment paper. Refrigerate covered overnight.
To bake, place dough portions 2" apart n parchment paper-lined baking sheets: let stand at room temperature 30 minutes before baking. Preheat oven to 400 F.
Bake 10-12 minutes or until edges are golden brown (centers will be light Cool on pans 2 minutes. Remove to wire racks to cool.