Line two baking sheets with parchment. Chop chocolate into 1/4 inch chunks; set aside. In a medium bowl, sift together flour, ground ginger, cinnamon, cloves, nutmeg & cocoa powder.
In the bowl of an electric mixer, fitted with the paddle attachment, beat butter and grated ginger until whitened, about 4 minutes. Add brown sugar; beat until combined. Add molasses; beat until combined.
In a small bowl, dissolve baking soda in 1-1/2 tsp. boiling water. Beat half of flour mixture into butter mixture. Beat in baking-soda mixture, then remaining half of flour mixture. Mix in chocolate.
Turn out onto a piece of plastic warp. Pat dough out to about 1 inch thick; seal with wrap; refrigerate until firm, 2 hours or more.
Roll dough into 1-1/2 inch balls; place 2 inches apart on baking sheets. Refrigerate 20 minutes.
Preheat oven to 325 degrees F. Roll in granulated sugar. Bake until the surfaces crack slightly, 10 to 12 minutes. Let cool 5 minutes; transfer to a wire rack to cool completely.