Preheat the oven to 350 F. In a medium bowl, whisk together flour, cocoa powder, salt, baking soda, cinnamon and ginger. In a large bowl, mix together butter, sugar, and molasses until fluffy. Add in egg and vanilla extract and mix until smooth.
Add in the flour mixture and mix until it is fully combined. Evenly press the cookie dough into a greased 8-inch square baking dish. Bake for 20-25 minutes.