Puree the blackberries with a handheld immersion blender and set them aside. If you used heat to defrost frozen blackberries, ensure that they’re cool before adding to the dough.

In a medium bowl, cream the butter and sugar with an electric mixer until light and fluffy. Add the cooled blackberry puree and the vanilla. Beat well.

In a small bowl, whisk together the flour, baking soda, and salt. Add to the blackberry mixture and stir by hand until combined. Fold in the chocolate chips, reserving about ¼ of them to add to the cookies after baking.

The dough will be very soft. Cover the dough and place it in the fridge to chill for at least 30 minutes.

Preheat the oven to 350°F. Line a cookie sheet with parchment paper or a Silpat.

Roll tablespoonfuls of the dough into balls. Place them onto the cookie sheet and press down slightly.

Bake the cookies for 8-10 minutes or until the edges are set. Cool on the tray for a few minutes, and then press the remaining chocolate chips onto the cookies. Transfer to a cooling rack to cool completely.