Preheat the oven to 350°F (180°C). Line a baking sheet with parchment paper or a silicone baking mat.

Thaw the blackberries (if frozen), then puree them using a hand-held immersion blender. Let cool. You should have ½ cup of blackberry puree.

In a medium bowl, cream the butter and sugar using an electric mixer until light and fluffy.

Add the blackberry puree and vanilla extract to the butter mixture. Beat well to combine.

In a separate bowl, whisk together the flour, baking soda, and salt. Add the dry mixture to the wet and stir by hand until fully incorporated.

Fold in the chocolate chips, reserving ¼ of them to use after baking.

Cover the dough and chill for at least 30 minutes.

Roll into tablespoon-sized balls, place on the prepared baking sheet, and press down slightly.

Bake for 8–10 minutes, or until the edges are set.

Remove from oven, press the remaining chocolate chips into the tops of the cookies, and allow them to cool on a rack.