1. Sift together flour, cocoa powder, baking soda, and salt in a bowl.

2. In the bowl of an electric mixer fitted with the paddle attachment, beat sugar and butter on medium speed until mixture is light and fluffy, about 2 minutes. Add eggs and vanilla, and beat to combine. Reduce speed to low, and gradually add flour mixture; beat to combine. Form dough into a flattened disk, and chill until firm, about 1 hour.

3. Preheat oven to 350 degrees. Shape dough into 1 1/4-inch balls. Roll each ball in sanding sugar. Place on baking sheets lined with parchment paper, about 1 1/2 inches apart. Bake until set, 10 to 12 minutes, rotating halfway through. Transfer to a rack to cool for 5 minutes. Transfer cookies from baking sheet to wire rack. The cookies can be stored between layers of parchment in an airtight container at room temperature for up to 1 week.