In a medium-sized bowl, whisk together the flour and cocoa. Set aside.
In another larger bowl, beat together the butter, sugar, and salt until light and fluffy, about 1 to 2 minutes.
Add the flour-cocoa mixture to the beaten butter, a few tablespoons at a time, and continue to mix until all of the flour is incorporated. The mixture will look quite crumbly, however, the dough is actually quite pliable.
Line a work surface with a large piece of wax paper.
Dump the chocolate cookie dough onto the wax paper and begin shaping it into a log with your hands. Roll the log, flattening the edges of it as you go, until it is smooth, and about 7-inches (18-cm) long.
Move the cookie dough log down to the bottom edge of the sheet of wax paper. Roll the dough completely in the paper. Once rolled, twist the ends of the paper to secure.
Place the wrapped cookie dough log in the freezer for 15 to 20 minutes.
Preheat the oven to 325ºC (160ºC) and line a standard baking sheet with parchment paper.
Remove the chilled cookie dough from the freezer and slice it into approximately 24 ¼-inch (6-mm) cookies. Some of the cookies will be thicker than others, while some will be more round. This is totally normal. The cookies will smooth and round out a bit as they bake.
Evenly space all of the cookie dough slices on the prepared parchment-lined baking sheet.
Bake the cookies in the preheated oven for 18 to 20 minutes.
Transfer the baking sheet to a wire rack and cool the cookies completely on the sheet before filling and sandwiching with frosting. Pictured is vanilla frosting and we dipped the edges of our cookies in crushed candy canes.