Preheat the oven to 400 ºF (200 °C). Line two large sheet pans with parchment paper.
In a medium bowl, whisk together the flour, salt, and baking soda. Set aside.
In a large bowl, using an electric hand mixer, cream together the butter, the granulated sugar, and the brown sugar until it's very light and fluffy.
Add the egg and the vanilla, and mix well until the mixture is light and fluffy again. Make sure to clean down the sides of the bowl as needed with a big spatula.
Dump in the whisked dry ingredients, and incorporate them either with the hand mixer on low, or by hand with a big wooden spoon.
Mix in the chocolate and the chopped walnuts. The dough should be quite thick.
Scoop approximately 50 gram portions of the dough, rolling them into balls.
Place 8 cookies per cookie sheet, being sure to space them apart and stagger them.
Bake the cookies one sheet pan at a time until the edges just begin to brown (this takes about 12 to 14 minutes). You might want to rotate the pan partway through the baking to make sure the cookies brown evenly.
Let the cookies cool completely on the sheet pan while you bake the second pan.
Store in an airtight container.
Notes
I baked these cookies at 400 °F to ensure they stay thick. Feel free to bake a test cookie at this temperature to make sure you like the results and adjust the temperature accordingly. lower the oven temperature to 375 or even 350 °F for thinner cookies.
whole wheat flour: 190 grams (1.5 cups) whole wheat flour to make whole wheat chocolate chip cookies—note that at 190 grams (1.5 cups) of whole wheat flour, the cookies spread out more than they would with the same weight of all-purpose, but they are still on the thicker side so I don't think you should add more flour than this.
rye flour: 190 grams (1.5 cups) rye flour to make rye chocolate chip cookies (basically replace with the same amount)—any more rye flour makes the cookies too thick and way too chewy, and less rye flour results in a much thinner cookie that spreads out. Also note that chocolate chip cookies made with 100 % rye flour will be quite chewy, even freshly baked.
oat flour: 220 grams–250 grams (1.75 cups to 2 cups) oat flour depending on how thick a cookie you want (note you can also replace the chopped chocolate with raisins to make them gluten-free oat flour raisin cookies )
corn flour: 220 grams–250 grams (1.75 cups to 2 cups) corn flour, depending on how thick a cookie you want
buckwheat flour: 310 grams (2.5 cups) buckwheat flour to make gluten-free buckwheat chocolate chip cookies—less works, but the cookies spread quite a bit!
If you want to garnish: you can't go wrong with a sprinkle of flaky sea salt which will help balance out the sweetness of the cookie dough.