Prepare the Baking Pan: Preheat the oven to 350°F. Grease a 9 × 9-inch glass baking pan, then line it with parchment paper. Set the prepared pan aside.
Melt the Butter: Place the butter in a microwave-safe bowl and heat until melted. Remove the bowl from the microwave, then stir in the sugar and dark molasses.
Heat the Butter Mixture: Return the bowl to the microwave and heat for 30 seconds. Stir, then microwave for another 60 seconds. The mixture should bubble slightly around the surface, but take care not to let it burn.
Add the Bittersweet Chocolate: Remove the bowl from the microwave and immediately stir in the 6 ounces of chopped bittersweet chocolate. Continue stirring until the chocolate melts completely. If a few pieces remain unmelted, microwave the mixture for an additional 15 seconds and stir again. Cool the Chocolate Mixture: Allow the melted chocolate mixture to cool slightly before adding the eggs. This helps prevent the eggs from cooking when they are incorporated.
Incorporate the Eggs and Ginger: Whisk in 2 or 3 room-temperature eggs, depending on your preferred brownie texture. Add the freshly grated ginger and mix until evenly incorporated.
Combine the Dry Ingredients: In a large mixing bowl, combine the all-purpose flour, cocoa powder, baking powder, cinnamon, and salt. Stir until the dry ingredients are evenly distributed.
Mix the Brownie Batter: Pour the chocolate mixture into the bowl of dry ingredients. Stir just until everything is combined, avoiding unnecessary mixing.
Add the Optional Chocolate: Fold in the additional 1/2 cup of chopped bittersweet chocolate if desired, distributing the pieces throughout the batter.
Fill the Baking Pan: Transfer the brownie batter to the prepared 9 × 9-inch glass pan. Spread it into an even layer.
Bake the Brownies: Place the pan in the preheated 350°F oven and bake for 45 minutes. Check the center by inserting a knife; it should come out mostly clean. A little moist batter is acceptable because it helps maintain the brownies' fudgy texture.
Cool the Brownies: Remove the pan from the oven and let the brownies cool for 15 minutes before removing them from the pan.
Slice and Serve: Cut the brownies into 9 large squares and serve.