First, preheat your oven to 350°F.
Next, add your blueberries to your mixing bowl. (If you are using frozen blueberries, smash them around a little with your mixer. This will help break up the big blueberries into smaller pieces and mash some of the juices out. If you are using fresh or dried blueberries, give them a rough chop so that they are easier to smush around in the dough.)
Now, add your oats and mash them up with the blueberries.
Lastly, add your flour, eggs, kosher salt, peanut butter, and cinnamon.
Mix together until everything is mostly combined - it will be a bit dry and crumbly. Add about ⅛ cup of warm water to the dough, and mix until it sticks together in a ball. If the dough still seems dry, continue adding warm water in ⅛ - ¼ cup increments.
Next, flour a clean surface to roll out your dough with a rolling pin (or a bottle of wine - no one here is judging.)
Roll the dough out to about ½ an inch thick. It doesn't have to be perfect, but you don't want to make these really thin or they will burn. If you make them a little too thick, you can get away with just cooking them for a little longer.
Next, cut out your treats using your favorite cookie-cutters. (If you don't want to use a cookie-cutter, you can also use a pizza cutter or sharp knife and just cut 1 x 1-inch squares or 1 x 2-inch rectangles. )
Place your cookies on a cookie sheet lined with parchment paper or a non-stick baking mat. They don't have to be spaced too far apart because they won't really expand, but they will stick together if they are touching.
Bake in the oven at 350°F for 40 minutes, until the biscuits are hard/crunchy.
Let the treats cool off, then share with your favorite pup!