Direction :

1. Whisk the flour, cocoa and baking soda together.
2. Working with a stand mixer fitted with a paddle attachment, or with a hand mixer in a large bowl, beat the butter on medium speed until soft and creamy. Add both sugars, the salt and vanilla extract and beat for 2 minutes more.
3. Turn off the mixer. Pour in the flour, and mix just until the flour disappears into the dough — for the best texture, work the dough as little as possible once the flour is added, and don’t be concerned if the dough looks a little crumbly. Toss in the chocolate pieces and mix only to incorporate.
4. Turn the dough out onto a work surface, gather it together and divide it in half. Working with one half at a time, shape the dough into logs that are 1½ inches in diameter. Wrap the logs in plastic wrap and refrigerate them for at least 3 hours. (The dough can be refrigerated for up to 3 days or frozen in 1-ounce portions for up to 2 months. If you’ve frozen the dough, you needn’t defrost it before baking — just bake the cookies 1 minute longer.)
5. Center a rack in the oven and preheat the oven to 325º F. Line two baking sheets with parchment or silicone mats.
6. Working with a sharp thin knife, slice the logs into rounds that are ½-inch thick or that weigh exactly 1 ounce. (The rounds are likely to crack as you’re cutting them — don’t be concerned, just squeeze the bits back onto each cookie.) Arrange six rounds on a baking sheet, leaving about one inch between each round.
7. Bake the cookies one sheet at a time for 12 minutes — they won’t look done, nor will they be firm. Transfer the baking sheet to a cooling rack and let the cookies rest until they are only just warm, at which point you can serve them or let them reach room temperature.
8. Serve with milk after dinner or with morning coffee.