Combine dry ingredients in a mixing bowl. Cut in shortening. Make a well in the center and add water, a small amount at a time, to form a dough. Knead dough in bowl until it is smooth and feels elastic. Cover and set aside for ten minutes. Form dough into egg-sized balls and flatten between palms. With rolling pin, roll each ball into a 6 inch circle, about 1/8 inch thick. Cook on preheated ungreased skillet over medium high, approximately two minutes on each side, until tortilla looks slightly speckled. Cover with a clean towel to keep warm and soft until served. The tortillas may be cooled and stored in plastic bags in the freezer for later use.