Preparation

• Make the blueberry mixture. Add the blueberries and sugar into a small saucepan. Cook over medium heat while stirring frequently until the mixture has reduced by about half. Stir in lemon juice. Create a slurry with 1 tablespoon of blueberry juices and corn starch, then pour into the saucepan. Stir and boil for 10 seconds, then let cool and refrigerate.
• Make the cookie dough. Combine butter, sugars, lemon zest, and vanilla in a large bowl. Beat with an electric mixer until pale and fluffy.
• Beat in the egg until well combined. In a medium bowl, whisk flour, baking soda, baking powder, and salt. Add dry ingredients to the butter mixture and mix gently until incorporated. Fold in white chocolate chunks.
• Divide the dough in half. Mix the blueberry mixture into the dough in portions to minimize over-mixing, maintaining a marbled look.
• Chill the dough while preheating the oven to 350°F. Line cookie sheets with parchment paper.
• Use a 1 oz cookie scoop to place mounds of dough on prepared sheets, spacing them 3 inches apart. Bake for 14-16 minutes until edges are browned and tops are golden.
• Let the cookies cool for a minute on the sheets before transferring them to a wire rack.