Preheat oven to 375°F/190°C. Line two pans with parchment paper.
In a large bowl mix together flour and baking soda. Set aside.
In a large bowl using a hand mixer or a stand mixer fitted with the paddle attachment beat together butter, brown sugar, granulated sugar, and salt for 3-4 minutes until creamy. Add eggs and vanilla extract and beat until combined. Add flour mixture and beat on low speed just until combined. Don’t over mix. Add chocolate chips and walnuts and keep beating on low just until combined. The less you mix, the softer the cookies will be.
Drop rounded balls of dough (try not to pack them too much into a ball, rather leave them a bit fluffy and only shape the bottoms into rounds), about 6 oz. per cookie (or 8 pieces in total), onto prepared baking sheets, placing 4 cookies in each pan. Bake for 18-23 minutes, until cookies are browned at the edges and very slightly browned at the top, and the center is still soft. Allow to cool for 15 minutes in pan, then transfer cookies to a wire rack to cool completely.
Store cookies in an airtight container at room temperature for up to 2 days or in the fridge for up to one week (but serve them at room temperature). Cookies can also be frozen for up to 3 months. To thaw, leave on the counter, still covered, or overnight in the fridge.