Grease and flour a 10 inch tube pan. Mix together the flour and salt. Set aside.
Combine the evaporated milk and whole milk; Set aside. In a large bowl, cream together the butter, shortening and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the butternut flavoring. Beat in the flour mixture alternately with the milk, mixing just until incorporated.
Pour batter into prepared pan. Bake at 325 degrees F (165 degrees C) for 1 hour and 45 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool.