Preheat oven to 350°.
Combine first 3 ingredients in a large bowl; beat with a mixer at medium speed until well blended (about 1 minute). Add eggs, 1 at a time, beating well after each addition. Stir in molasses.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 7 ingredients (through salt) in a large bowl. Add flour mixture and 1 cup hot water alternately to sugar mixture, beginning and ending with flour mixture. Spoon batter into a 13 x 9-inch baking pan coated with cooking spray. Bake 30 minutes or until a wooden pick inserted in center comes out clean. Cool in pan. Cut into 12 squares; sprinkle with powdered sugar and serve with apple, if desired.