Mexican Whole Wheat Flour Tortillas

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.
Make balls the size of golf balls, about 2 ounces each. Place them on a tray, and cover with a cloth. Let stand for at least 1 hour, or up to 8 hours.
Heat a griddle or large frying pan over high heat. On a lightly floured surface, roll out a tortilla to your preferred thinness. Fry one at a time. Place on the griddle for 10 seconds, as soon as you see a bubble on the top, flip the tortilla over. Let it cook for about 30 seconds, then flip and cook the other side for another 30 seconds. Roll out the next tortilla while you wait for that one to cook. Repeat until all of the balls have been cooked. Tortillas can be refrigerated or frozen.