Add half of the buttermilk to the mixture and begin to mix on low speed then gradually add the rest of the buttermilk. Stop mixing when the dough is rough and shaggy.
Transfer dough to a lightly floured surface then divide in half and shape into 2 discs. Wrap each in plastic wrap and refrigerate for at least one hour or up to 3 days.
Combine the cornstarch and water in a small bowl to create a slurry. Stir the slurry into the blueberry mixture then cook for 1-2 more minutes or until thickened
Roll out pie dough to 1/4 inch thick then cut out ghosts. Place onto a baking sheet then scoop 1/2 tbsp of blueberry filling in the center of each one.