Sift flour, baking soda and cocoa powder.
Beat butter with a hand mixer or a stand mixer fitted with paddle attachment until light and fluffy. Add the sugars and beat for 2 minutes until well incorporated.
Add vanilla extract and salt. Mix well.
Add the dry ingredients and beat until everything comes together. Try not to over beat the dough. Finally add the chocolate chips and mix to incorporate.
Divide the dough into 2 equal pieces. Form a log of 1½" thick, wrap it well in plastic wrap and refrigerate for at least 3 hours or up to 3 days. They can also be frozen to bake off later.
Preheat the oven to 325°F.
Using a sharp knife, cut the log into ½" thick slices and place them 1" apart on a baking sheet. Bake for 12 minutes. Cookies will not be firm or hard. Cool them on a wire rack before serving.