Preheat the oven to 375°F (190°C) and prepare a baking sheet with parchment paper.

Cream together the softened unsalted butter, brown sugar, and white sugar until light and fluffy.

Add the eggs and vanilla, mixing until combined and creamy.

In a separate bowl, whisk together flour, baking powder, baking soda, cinnamon, and salt.

Gradually add the dry mixture to the wet ingredients, stirring gently to combine.

Fold in the old-fashioned rolled oats and refrigerate the dough for 30 minutes.

After chilling, fold in the frozen blueberries carefully.

Scoop tablespoon-sized balls of dough onto the baking sheet, spacing them apart.

Bake for approximately 15 minutes until edges are golden and centers look slightly underbaked.

Cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.