In a small bowl, combine flour, salt, baking powder, and cornstarch. Set dry ingredients aside.
In a large bowl, using a handheld electric mixer on medium speed, beat butter and white sugar for 1 to 2 minutes or until fluffy and well combined.
Add egg and 1 teaspoon of vanilla extract into the butter mixture. Continue to mix for another minute until the batter is smooth.
Add flour mixture to the wet ingredients and mix until just combined. Your batter will be very thick.
Mix in ½ cup of white chocolate chips.
Using a rubber spatula, gently stir in the fresh blueberries, being careful not to crush them. Remember your mixture will be very thick and a bit crumbly. Set aside while you make your cream cheese filling.
In a small mixing bowl, mix together cream cheese, powdered sugar, and 1 teaspoon vanilla extract until fully combined. Set aside.
Line two baking sheets with parchment paper.
Gently scoop 1 tablespoon of dough and form it into a ball with your hands. Be careful not to crush the blueberries as you’re forming the balls.
Make an indentation in the dough ball, forming a small bowl of sorts. Place the ‘dough bowl’ on your prepared baking sheet 2 to 3 inches apart. Repeat until you have formed 14 to 16 ‘dough bowls’. You should have excess dough remaining to top your cookies once filled with the blueberry pie filling and the cream cheese mixture. Scoop about 1 teaspoon of the cream cheese filling and 1 teaspoon of the blueberry pie filling into the center of the dough ball.
Use a bit more dough to seal over the filled ‘dough bowl’. Gently close up the dough and roll it around gently in your hand to seal in the filling so that it does not leak out when baked. Place the dough ball back on the cookie sheet.
Repeat this process until all the cookie dough balls are filled and shaped. Press a few white chocolate chips and/or blueberries into the top of each cookie ball. This makes a pretty finished cookie. Place cookie sheets into the freezer for 2 hours to chill before baking.
Preheat oven to 375°F. Bake the chilled cookies for 15 minutes or until just lightly golden brown around the edges and the center is set. Allow cookies to cool for 2 to 3 minutes on the cookie sheet before removing to a wire rack to cool the rest of the way.