When these cookies are cool, be sure to seal them up real tight in something like Tupperware or a Ziploc bag. That's the way to keep them moist and chewy like the original GrandMa's Big Cookies. In fact, he real product claims to be the only national cookie brand that guarantees the freshness of the product or double your money back. That confident gurantee comes from the current manufacturer, Frito-Lay, which purchased the GrandMa's Cookies brand from General Mills back in 1980.
Source: Even More Top Secret Recipes by Todd Wilbur.
Update 1/13/17: For an improved recipe, replace the 1/2 cup shortening with 3/4 cup softened unsalted butter. Also, reduce the baking soda to 1 1/2 teaspoons. 2 teaspoons is too much. Also, raising the oven temperature a little—to 300 degrees F—will help with browning and still keep the cookies chewy. Bake for 15 to 18 minutes.