01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - Whisk together the flour, baking soda, and salt in a medium bowl.
03 - Beat the softened butter with granulated sugar and brown sugar until light and creamy, approximately 2 minutes.
04 - Add the egg and vanilla extract to the butter mixture and beat until fully combined.
05 - Gradually mix in the dry ingredient blend until just combined, avoiding overmixing.
06 - Gently fold in the mixed berries and white chocolate chips, taking care not to crush the berries.
07 - Scoop tablespoon-sized portions of dough onto the prepared baking sheets, spacing them about 2 inches apart.
08 - Bake for 10 to 12 minutes until edges are golden and centres remain soft.
09 - Allow cookies to cool on the baking sheet for 5 minutes, then transfer to a wire rack. Serve warm.