Preheat oven to 350°. Butter a large baking sheet and set aside. In a medium bowl, whisk flour, cocoa powder, ginger, baking soda, cinnamon, nutmeg, and salt until thoroughly combined. Set aside.
In a large bowl, beat 3/4 cup butter and the brown sugar until light and fluffy, about 3 minutes. Add molasses, egg, and vanilla; beat to combine.
Mix in dry ingredients gently but thoroughly, scraping down sides of the bowl as necessary. (Batter will be thick.) Stir in chopped chocolate until well combined.
Form batter into 2-tbsp. balls, roll each ball in granulated sugar, and place 12 balls on buttered baking sheet. (If batter is too sticky, dampen your hands with water when forming balls.) Dip the bottom of a cup or glass in water and use it to flatten balls to a thickness of about 1/4 in., rewetting glass as necessary to prevent sticking.
Bake cookies 5 minutes, turn pan 180°, and bake until just set, about 5 minutes more. Cool on pan for 5 minutes, then transfer to cooling racks. Repeat forming and baking with remaining balls of dough.
Note: Nutritional analysis is per cookie.