In a large bowl, stir together 1 cup all-purpose flour, the whole wheat flour, and salt. Rub in the shortening by hand until the mixture is the texture of oatmeal. Make a well in the center, and pour in the boiling water. Mix with a fork until all of the water is evenly incorporated. Sprinkle with a bit of additional flour, and knead until the dough does not stick to your fingers. The dough should be smooth.