Preheat your oven to 375°F (190°C).

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

Add the eggs one at a time, then mix in the vanilla extract.

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

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

Fold in the frozen blueberries gently.

Scoop portions onto a lined baking sheet, spaced 2 inches apart.

Bake for approximately 15 minutes or until golden-brown on the edges.

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