1. In the bowl of a stand mixer, or by hand, beat the butter, brown sugar, and granulated sugar just until smooth and creamy.
2. Beat in the egg and the vanilla.
3. In a small bowl, whisk together the flour, baking soda, and salt.
4. Stir the flour mixture into the beaten butter until combined, then mix in the chopped chocolate (including any chocolate dust) and the chopped nuts.
5. Cover and chill the batter until firm. (It’s preferable to let it rest overnight in the refrigerator.)
6. To bake the cookies, preheat the oven to 350ºF (180ºC). Line two baking sheets with parchment paper or silicone baking mats.
7. Form the cookie dough into rounds about the size of a large unshelled walnut. Place the mounds evenly spaced apart on the baking sheets, and press down the tops to flatten them so they are no longer domed and the dough is even.
8. Bake the cookies for ten minutes, rotating the baking sheet midway during baking, until the cookies look about set, but are not browned.
9. Remove from the oven and quickly tap the top of each with a spatula, then return to the oven for two to five more minutes, until the tops of the cookies are light golden brown.
Remove from oven and let cookies cool.