Preheat the oven to 375 degrees F (190 degrees C).
In a bowl, combine the flour, brown sugar, and shortening. With your fingertips, rub these ingredients together until the shortening resembles small lima beans. Set crumb mixture aside.
In another bowl, dissolve the baking soda in the boiling water. Add the corn syrup and molasses; stir to blend. Pour filling into the shell, and sprinkle the crumb mixture over the top.
Bake in the middle of the oven for 10 minutes. Reduce the heat to 350 degrees F (175 degrees C); bake for 25 minutes more. The filling is set, but still quivers when the pan is little tapped. Do not over bake. Cool on a rack to room temperature.
