In a small bowl, mix flour, brown sugar, and butter or margarine together until it resembles course corn meal. Measure out 1/2 cup, and set aside for topping.
In a separate bowl, beat the egg. Mix in molasses and cold water. Add crumb mixture, and stir thoroughly. Stir baking soda into hot water, and then add to the molasses mixture. Mix well. Pour filling into pie crust, and evenly sprinkle the reserved topping on top.
Bake at 375 degrees F (190 degrees C) for 35 minutes.
