Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.
In a large mixing bowl, cream together the softened butter, cream cheese, and granulated sugar until smooth and fluffy.
Mix in the egg and vanilla extract until fully incorporated.
Gradually add the dry ingredients to the wet mixture, stirring until just combined.
In a separate small bowl, combine the fresh blueberries with lemon juice and powdered sugar, gently mashing them with a fork to create a chunky blueberry sauce.
Fold half of the blueberry mixture into the cookie dough until just swirled through, ensuring not to overmix.
Drop tablespoons of the cookie dough onto the prepared baking sheet, leaving space between each cookie.
Using a toothpick or small spatula, dollop the remaining blueberry mixture onto each cookie and gently swirl it in for a marbled effect.
Bake in the preheated oven for 10-12 minutes or until the edges are lightly golden.
Remove from the oven and let cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.
Notes
Serve the cookies on a beautiful plate, dusted with a little extra powdered sugar and a few fresh blueberries scattered around for a pop of color.