Preheat oven to 350°F (177°C). Line a large cookie sheet with parchment paper or silicone baking mat.

Add quick oats to a food processor. Pulse oats until they become very small and fine and start to partially become flour consistency. See photo in post for reference. I pulsed mine on high for about 30 seconds. If you are unsure if your oats are fine enough, it's better to pulse them a little longer. The smaller they are, the crispier the cookies will be.

Add oats, peanut butter and maple syrup to a large mixing bowl. Make sure you scrape the food processor and get all of the oat powder that sticks to the sides into your bowl. Make sure to also scrape all the maple syrup into your bowl as well as a lot of it gets stuck to the measuring spoon or measuring cup. Mix with a spatula until the ingredients are fully and evenly incorporated and the dough thickens to the consistency of cookie dough.

If using fresh blueberries, wash and thoroughly pat them dry. Cut them in half. Gently fold them into the dough with your spatula. It will be a little difficult because the dough is firm but just do your best not to crush the berries too much and fold them so they are evenly distributed throughout the dough. If using dried blueberries, just add them directly in (no need to cut them) and fold them into the dough.

Using a 1.5 tbsp cookie scoop, scoop dough onto the prepared cookie sheet, spacing the dough balls about 2 inches apart. Use the back of a metal spoon to flatten the dough balls into round disks and smooth the edges. You want the cookies to be fairly thin, between 3/16 inch to ¼ inch thick. The cookies do not spread much during baking, so shape them as you want the final outcome to be. Try your best not to squish the fresh berries too much because you don't want the dough to get too wet. If your dough is too sticky, you can wet the spoon before using it to flatten and shape.

Bake cookies for 13-15 minutes or until the surface and edges are brown. The browner the cookies are, the crispier they will be so try to bake until they are light or medium brown all over but be careful not to let the edges get too dark. Let cookies cool completely on the baking sheet before trying to remove them. They will crisp up further as they cool. Cookies with fresh blueberries are best enjoyed right away but leftovers can be stored in the freezer. Cookies with dried blueberries can be stored at room temperature for a few days and longer in the freezer.