How to Make It
Preheat oven to 350°F. Beat butter and brown sugar in a stand mixer fitted with a paddle attachment on medium speed until smooth, about 1 minute. Add egg, and beat until just combined. Beat in molasses and vanilla.
Stir together flour, cocoa, crystallized ginger, baking soda, cinnamon, salt, and ground ginger in a bowl. Gradually add flour mixture to butter mixture, beating on low speed until just combined, about 1 minute. Fold in chocolate.
Shape dough into 30 (1 1/2-inch) balls (dough will be sticky). Place granulated sugar in a bowl; roll balls twice in granulated sugar. Arrange balls 2 inches apart on 2 baking sheets lined with parchment paper.
Working in 2 batches, bake in preheated oven until tops are crackly but cookies are still soft to the touch, 10 to 12 minutes. Cool on baking sheets 5 minutes. Transfer to wire racks; cool completely, about 30 minutes.