These dog biscuits have a bit of protein from peanut butter and some abrasiveness from bran flakes and oats. I use a mostly-oat low-fat granola in place of just the oats and the kind of bran cereal with flax seeds in for some extra texture.
Preheat oven to 350° F.
Mix the peanut butter, stock, and oil into the egg until smooth. Mix the flour, cereal and oats together. Add the dry ingredients to the egg mixture until it forms a very stiff dough (you'll need to use your hands at the end. If not very stiff, add flour gradually.
Turn the dough out onto a lightly floured surface and roll to about ¼ inch thick. Cut out shapes (bone shapes work well!) and bake on lightly greased cookie sheet in the middle rack for about 15 minutes. Best results are obtained by allowing biscuits to harden overnight.