Pre-Heat oven to 350 degrees. Grease a 13x9 inch baking pan.
Using a large bowl, stir the flour,brown sugar,and salt together. Add the butter. Work the butter into the mixture until you have crumbs using a pastry blender or rubbing the mixture together with your fingers. Take out 1 1/2 cups of crumbs, reserve for the topping.
In a large bowl combine the boiling water,molasses and baking soda, mix well with a whisk. Make sure to use a large bowl, when the baking soda is added it foams up quiet a bit.
Add 1/2 the liquid to the crumb mixture. Mix until moist and smooth. Add the remaining liquid and mix until just incorporated, the batter will be slightly runny.
Pour the batter into your prepared pan, top with reserved crumbs. press crumbs into the batter lightly. Bake 45 minutes or until a tooth pick inserted in the center comes out clean.