Thaw blackberries if frozen, then puree until smooth. Cool the puree.

Cream together softened butter and sugar until light and fluffy. Stir in blackberry puree and vanilla.

Whisk flour, baking soda, and salt together. Gradually mix this into wet ingredients until just combined. Fold in chocolate chips.

Chill the dough for at least 30 minutes in the refrigerator.

Scoop and roll dough into balls, flatten them slightly, and arrange on a lined baking sheet.

Bake at 350°F for 8-10 minutes, until edges are set and centers are slightly soft. Add reserved chocolate chips halfway through baking.

Allow cookies to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.