In a large mixing bowl, beat the brown sugar and lemon zest together until they are the consistency of wet sand. Beat butter and lemon sugar together until light and fluffy. This takes about 2-3 minutes on medium speed.
Evenly pour the molasses cake batter into the prepared pan. Bake the ginger cake for 28 - 32 minutes or until a toothpick inserted into the center of the cake comes out clean or with a few moist crumbs.