Preheat your oven to 350°F (180°C) and line a baking sheet with parchment paper.

If using frozen blackberries, thaw and puree until smooth.

Cream together softened butter and granulated sugar until light and fluffy, then mix in blackberry puree and vanilla.

In a separate bowl, whisk together flour, baking soda, and salt, then fold into the wet ingredients.

Cover and refrigerate the dough for at least 30 minutes.

Scoop tablespoonfuls of dough, roll into balls, and place on the baking sheet, lightly flattening each ball.

Bake for 8 to 10 minutes or until edges are set and centers are slightly soft.

Cool on the baking sheet for about 5 minutes before transferring to a wire rack.