In a large bowl, cream the butter, brown sugar and sugar until light and fluffy.
Beat in eggs and vanilla. Combine the flour, baking soda and salt; gradually add to creamed mixture and mix well. Stir in chocolate chips and walnuts.
Shape quarter cupfuls of dough into balls. Place in an airtight container, separating layers with waxed or parchment paper; cover and refrigerate overnight.
To bake, place dough balls 3 inches apart on parchment paper-lined baking sheets. Press a shallow indentation in the center of each with your thumb, reshaping sides to smooth any cracks. Let stand at room temperature for 30 minutes.
Preheat oven to 400°. Bake for 10-12 minutes or until edges are golden brown. Cool for 2 minutes before removing from pans to wire racks; cool.