Whisk together the dry ingredients—flour, baking soda, salt, cocoa powder, ginger, cinnamon, nutmeg and all spice. Set aside.
Beat butter and brown sugar together until light and fluffy. Add the egg and mix until combined. Add the molasses and mix until combined. Scrape down the bottom and sides of the bowl as necessary.
Alternate adding the flour and milk to the batter. Add half the flour mixture and mix just until combined. Add all the milk and mix until incorporated. Finally add remaining flour and mix until combined.
Transfer batter to prepared pan. Bake at 350° F for 50 to 60 minutes or until a tooth pick inserted in the center comes out with little to no crumbs. Cool in the pan for 15 minutes then invert to a wire rack to cool completely. Garnish with a dusting of confectioners' sugar and cranberries if desired.
Store gingerbread in an airtight container at room temperature for 3 days or in the refrigerator for 5 days.How to freeze gingerbread: Let the loaf cool completely. Wrap it securely in plastic wrap or aluminum foil. Place in a freezer-safe bag and store in the freezer for 1 month. Defrost in the refrigerator before bringing to room temperature and serving.Gingerbread muffins: Preheat oven to 375° F. Line a muffin tin with paper liners. Divide batter evenly among cups. Bake for 15 to 20 minutes.Recommended tools: Kitchen scale, hand mixer and loaf pan