In a large mixing bowl, use an electric mixer to beat the softened unsalted butter and granulated sugar on medium speed for about 2 minutes until light and fluffy. Add the egg, vanilla extract, salt, and baking soda; mix until smoothly incorporated.

Gradually sift in the all-purpose flour while mixing on low speed. If the dough appears crumbly, add up to 2 tablespoons of milk, mixing until you achieve a soft dough.

Gently fold in the white chocolate chips, ensuring even distribution. Carefully incorporate the fresh blueberries using a spatula to avoid crushing them.

Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper. Drop rounded tablespoonfuls of dough onto the sheet, keeping them about 2 inches apart. Bake for 10 to 12 minutes, until edges are lightly golden.

Let the cookies rest on the baking sheet for 2 minutes, then transfer them to a cooling rack to cool completely. Store in an airtight container at room temperature for up to 3-4 days.