Make the Blueberry Swirl: In a small saucepan, combine blueberries, sugar, and lemon juice. Cook over medium heat for 5–7 minutes, stirring occasionally, until the mixture thickens like jam. Remove from heat and let it cool completely.

Make the Cookie Dough: In a large bowl, beat butter, cream cheese, granulated sugar, and brown sugar together until light and fluffy. Add the egg and vanilla, mixing until smooth.

Add Dry Ingredients: In a separate bowl, whisk flour, baking powder, baking soda, and salt. Gradually add to the wet ingredients and mix on low until a soft dough forms.

Swirl in Blueberries: Gently fold the cooled blueberry mixture into the dough with a spatula to create streaks — don’t overmix.

Chill the Dough: Scoop dough into balls using a medium cookie scoop and place on a baking sheet. Chill for 30 minutes to help the cookies hold their shape.

Bake: Preheat oven to 350°F (175°C). Bake cookies for 12–14 minutes, until the edges are lightly golden and centers are soft. Let cool on the baking sheet for 5 minutes, then transfer to a wire rack.