Stir together water, oats, butter, and bouillon; allow to stand for 5 minutes.
Stir in milk powder, cornmeal, and egg until combined.
Stir in flour, 1/2 cup at a time, mixing well after each addition.
Turn dough onto a lightly floured surface and knead for 4 minutes, adding more flour if necessary to make a stiff dough.
Roll dough out to 1/2″ thick.
Cut shapes out of dough with a cookie cutter and place on a greased cookie sheet.
Bake in a 325 degree oven for 50 minutes.
Allow to cool and dry on wire racks.
Notes: Store in refrigerator up to 1 month OR freeze up to 1 year.
As noted in a comment from Nadine M. Rosin on a previous recipe: “since many dogs have an underlying gluten allergy, …substituting quinoa, spelt, or millet flour (from any health food store or natural market) in this great recipe is also very effective!”