If using frozen blackberries, allow them to thaw completely at room temperature. Puree until smooth and strain to remove seeds.

In a medium bowl, beat butter and sugar together until light and fluffy, then mix in blackberry puree and vanilla extract.

In a separate bowl, whisk together flour, baking soda, and salt. Gradually add to butter mixture, mixing until just combined. Fold in chocolate chips.

Cover dough with plastic wrap and refrigerate for at least 30 minutes.

Preheat your oven to 350°F (180°C). Roll dough into balls, flatten slightly, and place on a lined cookie sheet. Bake for 8–10 minutes.

Remove from oven, press reserved chocolate chips onto cookies, cool slightly, then transfer to a wire rack.