Preheat oven to 350 degrees. In a large bowl, mix together all ingredients and about 3 tablespoons water to form a dough.
Roll out mixture between two sheets of plastic wrap to ¼ inch thick. Remove plastic wrap and cut out biscuits with a small cookie cutter. Reroll scraps and continue cutting out biscuits.
Space biscuits 1 inch apart on a baking sheet. Bake for 30 minutes until browned and firm. Transfer biscuits to a wire rack. Turn off oven and place biscuits on wire rack in oven overnight.
Recipe by Rachel Schultz at https://rachelschultz.com/2012/09/20/homemade-dog-biscuits/