Cream butter and sugars together until smooth.
Add pudding, eggs, additional egg yolk and vanilla. Beat for about one minute on medium speed.
In a separate bowl, combine flour, baking soda, and salt.
Add dry ingredients to the wet ingredients a 1/2 cup at a time and mix until combined.
Fold in chocolate chunks and walnuts.
Mold into a giant ball and wrap tightly in plastic wrap.
Chill for at least two hours, overnight is best.
Scoop 1 1/2 tablespoon sized scoops onto a nonstick baking sheet about two inches apart. I use this kind of scoop.
Bake at 350 F for 10-13 minutes.
Cool on pan for a couple of minutes before transferring to a cooling rack.