In a small mixing bowl, sift the flour, cocoa and baking soda together. Set aside. In a stand mixer or with a hand mixer in a large bowl, beat the butter on medium speed until soft and creamy.

Add sugar, brown sugar, salt and vanilla extract and beat for 2 minutes more. Add half of the flour mixture and blend on low speed just until blended. Add remaining flour mixture and blend on low speed just until blended. Add chocolate chips and stir to combine.

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 1 ½ 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 for up to 2 months. If you’ve frozen the dough, you needn’t defrost it before baking–just slice the logs into cookies and bake the cookies 1 minute longer.)

Preheat the oven to 325 degrees F. Line two baking sheets with parchment or silicone mats. Use a sharp knife and slice the logs into rounds that are ½ inch thick. (If the rounds crack while you're cutting them, just press the pieces back onto each cookie.)

Place the rounds on the baking sheets, leaving about 1 inch between them. Bake the cookies about 12 minutes. The cookies should be firm around the edges but not in the center. Let the cookies cool 5 minutes on the baking sheet and then transfer to a rack to cool completely.