Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a mixing bowl, whisk together the flour, oats, baking soda, salt, and cinnamon.

In another bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.

Add the egg and vanilla extract to the butter mixture and mix until combined.

Gradually add the dry ingredients to the wet ingredients and mix until just combined.

Gently fold in the halved blackberries.

Drop tablespoon-sized portions of the dough onto the prepared baking sheet, spacing them about 2 inches apart.

Bake in the preheated oven for 10-12 minutes or until the edges are golden brown.

Remove from the oven and let cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.