How to Make It
In a medium bowl, whisk together the flour, cocoa, and salt.
Using an electric mixer, beat the butter and confectioners’ sugar on medium-high until fluffy; beat in the vanilla. Reduce speed to low and gradually mix in the flour mixture until just combined (do not overmix).
On a lightly floured surface or piece of parchment paper, roll the dough out ¼ inch thick. With a 2-inch cookie cutter (preferably fluted), cut the dough into rounds, flouring the cutter and rerolling the scraps as necessary. Arrange 1 inch apart on parchment-lined baking sheets. Refrigerate on the baking sheets for at least 2 hours and up to 1 day.
Heat oven to 350° F. Sprinkle the rounds generously with the coarse sugar and bake, rotating the sheets halfway through, until set, 20 to 22 minutes. Cool slightly on baking sheets, then transfer to wire racks to cool completely.