Preheat your oven to 350°F (175°C). Add blueberries to your mixing bowl. For frozen blueberries, smash them a bit; for fresh or dried blueberries give them a rough chop.

Add oats and mix them with the blueberries.

Add the remaining ingredients: flour, eggs, kosher salt, peanut butter and cinnamon. (Add optional ingredients if desired.)

Mix until mostly combined; it will be a bit dry and crumbly.

Add about 1/8 cup (30 ml) of warm water (or broth) and mix until it sticks together in a ball.

Add more water gradually if the dough remains dry.

Flour a clean surface; roll out the dough to about 1/2 inch (1.3 cm) thick.

Cut out treats using cookie cutters or a sharp knife.

Place cookies on a lined cookie sheet (with parchment paper or a non-stick mat).

Bake at 350°F (175°C) for 40 minutes until hard and crunchy.

Let cool before giving them to your dog.