Preheat oven to 350°. Grease and flour a 13x9x2-inch pan; set aside.
In a medium bowl, sift together flour, baking soda, ginger, baking powder, salt, and cinnamon; set aside.
In a large mixing bowl, combine brown sugar and butter; beat at medium speed with a mixer until creamy. Add sweet potato, milk, molasses, eggs, and vanilla, beating to mix well. Gradually add flour mixture to sweet potato mixture, beating until combined.
Spoon batter into prepared pan. Bake until a wooden pick inserted in center comes out clean, about 30 to 40 minutes. Let cool in pan for 10 minutes. Remove from pan, and cut into 12 squares. Serve warm with Maple Pecan Butter Sauce.