Preheat your oven to 350°F (175°C) to ensure even baking and perfect texture.
In a large mixing bowl, beat the softened unsalted butter and granulated sugar together using an electric mixer until light and fluffy, about 2-3 minutes.
Add the large egg and vanilla extract to the butter-sugar mixture and mix until well combined.
In a separate bowl, combine the all-purpose flour, baking powder, baking soda, salt, and ground cinnamon to evenly distribute the dry ingredients.
Gradually add the dry ingredients to the wet mixture, stirring until just combined to avoid tough cookies.
Gently fold in the rolled oats and fresh blueberries, ensuring even distribution throughout the dough.
Using a cookie scoop, drop tablespoonfuls of dough onto a parchment-lined baking sheet, spacing them about 2 inches apart.
Bake in the preheated oven for 12-15 minutes, or until the edges are lightly golden.
Remove from oven and let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.