Make sweet cream cheese mixture: Place 12 ounces cream cheese, ¾ cup powdered sugar, 1 egg yolk, 2 Tablespoons cornstarch, and 2 Tablespoons dried cranberries in a medium bowl. Stir well to combine.
Roll out 1 puff pastry sheet on a lightly floured work surface into a rectangle about 10x16 inches (25x40cm). Transfer the sheet of dough to lightly floured baking paper.
From top to bottom, lightly mark half of the rolled-out sheet. I used a skewer stamped on the dough sheet as a center dividing line.
Using a sharp knife, carefully make a few diagonal slashes in the left half of the dough.
Spread the sweetened cream cheese mixture in the middle of the right half, but leave at least 1 inch (3 cm) of empty space on the sides.
Brush all sides with 1 egg white left over from making the cream filling.
With the help of baking paper, fold the left side of the dough over the right half with the cream filling.
With a fork, press the edges where the folded dough ends meet.
Carefully transfer the finished shape with the parchment paper to the baking sheet. Fold down the edges, previously pressed with a fork. Brush egg white on the pastry surface.
Preheat oven to
350 °F and bake puff pastry with cream filling for 40 minutes until it turns golden brown.