Preheat oven to 350°F. Line a 9×9-inch baking dish with parchment paper. Set aside.
In a large bowl, combine butter and brown sugar. Stir well.
Mix in eggs, molasses, and vanilla.
In a medium bowl, whisk together the flour, ginger, cinnamon, baking powder, and salt.
Gradually stir the flour mixture into the butter and egg mixture until completely combined.
Spread the batter evenly into the prepared pan. Bake for 30-35 minutes, or until the edges are set and the center is no longer jiggly. If you are using a 9×13-inch pan, bake for 25-30 minutes.
Allow to cool completely before sprinkling with confectioners' sugar. Cut and serve!