Step 1

In a medium bowl sift together flour, baking soda and salt. Set aside.

Step 2

In a large bowl, place the melted butter, granulated sugar and brown sugar. Whisk until well combined. Whisk in the egg, egg yolk and vanilla extract. Add flour mixture and mix just until combined. Do not overmix. Fold in chocolate chips and walnuts.

Step 3

Chill the dough for at least 2 hours, preferably 6 hours or overnight (you can keep the dough in the fridge for up to 3 days).

Step 4

Preheat oven to 325F/165C degrees. Line pans with parchment paper.

Step 5

If the cookie dough is hard to handle, leave it on the counter for a few minutes.

Step 6

Drop rounded balls of dough onto prepared baking sheet, the size of 3 tablespoons each. Bake for 11-13 minutes, until cookies just begin to brown at the edges and center is still soft. Cookies will appear undone but will continue to bake on the warm baking sheet. Allow to cool for 10 minutes, then transfer to a wire rack to cool completely.

Step 7

Store cookies in an airtight container for up to 3 days. They can also be frozen for up to 2 months.