Using an electric mixer, cream together butter and 2 cups of the sugar. Add in eggs and vanilla; combine.
In a separate bowl whisk together flour, cocoa and baking soda.
Slowly add dry ingredients into wet ingredients until combined.
Place remaining ¼ cup sugar in a small bowl. Form dough into balls the size of a ping pong ball. Roll balls in the sugar bowl to coat.
Arrange rolled balls on a parchment lined cookie sheet, leaving plenty of room between them. Bake for 12 minutes. Remove to a cooling rack to allow to cool completely before storing in an airtight container.
Make ahead Tip: Roll dough into balls and place on a baking sheet lined with waxed paper. Pop into the freezer for 2 hours and then remove from the plate to a large freezer bag. When you’re ready to make the cookies, take them out of the freezer while the oven heats up to 350°F and then roll the cookies in the sugar. Place them on a parchment-lined baking sheet and bake for 15 minutes.