Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a large mixing bowl, cream together the softened unsalted butter and granulated sugar until light and fluffy, about 2-3 minutes.
Add the egg and vanilla extract to the butter and sugar mixture. Beat until fully combined.
Gradually add the blueberry muffin mix to the wet ingredients, mixing until just combined.
Gently fold in the fresh blueberries, being careful not to crush them.
Using a tablespoon or cookie scoop, drop rounded spoonfuls of dough onto the prepared baking sheets, spacing them about 2 inches apart.
Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden and the centers are set.
Remove the cookies from the oven and allow them to cool on the baking sheets for 5 minutes before transferring to a wire rack to cool completely.