In a small bowl whisk together dry ingredients: flour, corn starch, salt and baking powder, set aside.
Cream butter and sugar on high speed for about 2 minutes, until light and creamy. Add egg and vanilla and mix to combine.
Running your mixer on low, mix in dry ingredients mix.
Fold in about ¾ of the white chocolate chunks, and reserve the remaining to press on top of the cookies.
Finally, fold in blueberries with a rubber spatula, but do this very gently and try not to break the berries. The dough will be thick and sticky. Cover and refrigerate for 2 hours.
To make the filling, mix cream cheese, vanilla, and powdered sugar just to combine and place in the fridge.
When ready to bake preheat the oven to 350 F and line baking sheets with parchment paper.
To assemble the cookies, scoop one heaping Tablespoon of dough and make a deep bowl. Fill with 1 teaspoon of cream cheese mixture and about ¾ teaspoon of blueberry jam. Top with ½ Tablespoon of cookie dough and seal any openings. Roll gently to make a ball. Press a few white chocolate chunks on the top and sides of each cookie. Before baking freeze cookie balls for 10 minutes (if you don’t have enough space for a baking sheet in the freezer, place rolled cookies on a tray lined with parchment paper freeze, and transfer to a baking sheet when ready to bake)
Arrange cookie balls onto baking sheet leaving 3 inches apart, because the cookies will spread while baking. Bake 16-18 minutes. Cool on a baking sheet for 10 minutes, then transfer to a rack to cool completely.