Preheat the oven to 375 degrees F. Butter and flour a 13 x 9 inch baking pan. Beat the butter with an electric mixer until smooth. Graduall add the sugar and continue beating well after each addition. Add the molasses and beat until well blended. Add the ginger, zest, and spices. Add salt. Mix the soda with the vinegar in a small bowl and add to the batter. Transfer to a large bowl.
Add the flour by hand alternating with the milk, beginning and ending with the flour. After each addition stir only enough to combine. Spread the batter evenly into dish and bake for 55 to 60 minute.