Preheat oven to 325°F (160°C). Line a baking sheet with parchment paper.

If using fresh sweet potato, roast or microwave until very soft, then mash until smooth. Finely chop the kale and steam briefly (30–60 seconds) if desired to soften; squeeze out excess moisture.

In a large mixing bowl, combine the mashed sweet potato, egg, and olive oil. Whisk or stir until smooth; add 1–2 tablespoons water if mixture seems very thick.

In a separate bowl, whisk together oat flour, whole wheat flour, ground flaxseed, and baking powder until evenly blended.

Gradually add the dry mix to the wet mixture, stirring until a stiff dough forms. Fold in the chopped kale and, if using, the shredded chicken so they are evenly distributed. If dough is too sticky, add up to 2 tablespoons more oat flour; if too dry, add a teaspoon of water at a time.

Lightly flour a work surface with oat flour and roll the dough to about 1/4 inch (6 mm) thickness. Use a cookie cutter or knife to cut into shapes sized appropriately for your dog (smaller shapes for small dogs).

Place biscuits on the prepared baking sheet spaced 1 inch apart. Optionally brush the tops lightly with a tiny amount of olive oil and press a few small shreds of chicken on top for extra aroma.

Bake at 325°F (160°C) for 25–30 minutes, then flip each biscuit and bake an additional 10–15 minutes until edges are golden and biscuits are dry and crunchy. For extra crunch, turn off the oven and leave biscuits inside with the door slightly ajar for 20 minutes to cool gradually.

Allow biscuits to cool completely on a wire rack before offering to your dog; they will crisp as they cool. Test one for texture: it should be firm and break cleanly (not bendable).

Store cooled biscuits in an airtight container at room temperature for up to 7 days, or refrigerate up to 2 weeks. For longer storage, freeze in a sealed bag for up to 3 months and thaw before serving.