I've tried a bunch of different recipes with my Edith and our guests and I always end up coming back to the simplest because it's always a hit! I've even had clients ask if I would sell them, but I happily give away the recipe because I love the idea that we can all easily make healthy, yummy, preservative-free treats for so much cheaper than you can get them at the store.
My cookies literally only have 2 ingredients (unless you count water):
-- flour (I always use a grain-free variety to avoid common allergens -- usually some combination of brown rice flour, quinoa flour, and/or chick pea flour)
-- all natural peanut butter (I always buy the fresh-ground, nothing-but-ground-peanuts kind from the grocery deli -- no need to add a bunch of extra oil or sugar)
-- hot water
I usually eye ball my ingredients (this is a very forgiving recipe) -- I'd say about 3 parts flour, 1 part peanut butter, 1 part hot water.
In a stand mixer, mix together flour and peanut butter. Once combined, slowly add hot water just until dough forms. Roll out on floured surface, cut with your choice of cookie cutter, and bake at 375 until golden brown.
They're super simple, but VERY popular with the pups (Edith knows when I'm making them and conveniently posts herself in the kitchen until they're ready to be sampled) and seem to store remarkably well as long as they're totally cooked through. I keep them in an airtight container with a silica packet on my counter top and I've had them for as long as 2 weeks with no issue.