Pre-heat the oven to 350°F.
Cream together the shortening, butter and sugar until light.
Blend in the molasses and egg.
Dissolve the baking soda in 3/4 cup boiling water and add to the mixture; add the vanilla.
Sift together the dry ingredients and add gradually, mixing well to make a soft dough.
Cool.
Roll out to 1/2″ thickness. A little more flour may be added, but just enough to make the dough easy to handle.
Cut the cookies and place on greased cookie sheets.
Bake for 8-10 minutes.