Preheat your oven to 375°F (190°C) and prepare a baking sheet.

In a large mixing bowl, cream the softened unsalted butter until smooth.

Mix in the brown sugar and white sugar, then add baking powder, baking soda, cinnamon, and salt. Beat until fluffy.

Add in the eggs and vanilla extract, mixing until light and creamy.

Gradually stir in the all-purpose flour until just combined.

Fold in the old-fashioned rolled oats gently until evenly distributed.

Cover the dough and refrigerate for 30 minutes.

Gently fold in the frozen blueberries, being careful not to crush them.

Scoop about two tablespoons of dough for each cookie and place on the prepared baking sheet.

Bake for approximately 15 minutes until golden brown around the edges.

Let cool on the baking sheet for 10-15 minutes before transferring to a wire rack.