In a large bowl, whisk together the flour, cocoa powder and salt; set aside.
Using an electric mixer, beat together the butter and both sugars on medium speed until light and fluffy, about 5 minutes. Add the eggs and mix to combine, scraping the sides of the bowl as needed. Add the vanilla extract and again beat to combine. Reduce the speed to low, add the flour mixture, and beat until just combined, giving it a final mix by hand with a rubber spatula.
Divide the dough in two and shape each half into a round disk about 2 inches high. Wrap both in plastic wrap and refrigerate for at least 45 minutes (or up to 1 day).
Working with one piece of dough at a time, roll it out between two pieces of parchment paper (it's non-stick and eliminates the need for extra flour) to a ¼-inch thickness. Transfer the parchment and dough onto a cutting board or baking sheet and refrigerate for 15 minutes.
Meanwhile, preheat oven to 325 degrees F. Line baking sheets with parchment paper or silicone baking mats.
Remove the dough from the refrigerate and cut out your shapes and place on the parchment-lined baking sheets, leaving about 2 inches of space between them. Gather up any excess dough, re-roll and repeat process until all of the dough has been used.
Place the baking sheets with the cut-out cookies into the freezer for 15 minutes before baking.
Bake until the cookie edges are set, about 15 to 17 minutes. Remove from the oven and place the baking sheet on a cooling rack for 10 minutes, then use a spatula to transfer the cookies to the rack to cool completely. Allow cookies to cool completely before decorating. Cookies can be stored in an airtight container at room temperature for up to 2 weeks. Cookies can also be frozen - I wrapped them in plastic wrap and placed in a ziploc bag.