1Preheat oven to 350 degrees. Lightly grease a 9 X 13 inch pan. Combine flour, spices, and salt. In a small bowl, dissolve the baking soda in the hot water. Stir in the molasses.
2In a large bowl, cream the butter and brown sugar. Beat in the eggs. Beat in the molasses mixture. Gradually blend in the dry ingredients. Spread the dough into the pan. Bake for 18-20 minutes, or until a toothpick comes out clean.
3For the icing: Combine powdered sugar and milk until smooth and desired consistency. Frost bars while still warm. Cool before cutting.