Preheat oven to 350°F. Line a loaf pan with parchment paper. Whisk together 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.
Next, add the molasses and mix until combined. Scrape down the sides of the bowl.
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.
Dust with powdered sugar and enjoy!