Prep: Preheat oven to 350°F. Line baking sheet(s) with parchment paper.
Dry Ingredients: In a medium mixing bowl, whisk together flour, cornstarch, baking soda and salt. Set aside.
Cream: In the base of a stand mixer, add softened butter and brown sugar. Cream for 2 minutes with the paddle attachment on medium speed (you can also use a large bowl and a hand mixer). Next, add vanilla and egg. Mix until combined, on medium low speed (about one minute).
Add Dry Ingredients: Slowly add the dry ingredients to the wet ingredients and mix on low speed. Scrape down the bowl as needed. Do not over mix.
Add the Goodies: Using a silicone spatula, gently fold in white chocolate chips until evenly incorporated. Then, gently fold in blueberries.
Scoop & Drop: Scoop cookie dough using a medium sized cookie scoop or a large spoon (about two tablespoons). Carefully roll dough into balls and place on the prepared baking sheet about 2 inches apart.
Bake: Bake cookies in preheated oven for 9 minutes or until slightly golden brown around the edges. Try not to overbake! Cookies should still be slightly soft in the center--they will continue to set up as they cool.
Cool: Allow cookies to sit on the baking sheet for about 5 minutes before transferring them to a cooling rack