To make the pastries:

Cup of Yum
1. Preheat oven to 425˚F (220˚C). Line a baking sheet with parchment or lightly grease.
2. In a medium bowl, combine the brown sugar, cornstarch, and cinnamon.
3. In a small bowl, beat together egg yolk and milk to make the egg wash.
4. On a large floured work surface, gently roll out a sheet of the puff pastry until even with no cracks or creases.
5. Cut into 6 equal rectangles and transfer to the prepared baking sheet.
6. Divide the brown sugar cinnamon mixture among the rectangles, leaving a 1/2 inch (1.25 centimeter) border around the edges.
7. Brush the edges with the egg wash.
8. Gently roll out the second sheet of puff pastry until even with no cracks or creases. Cut into 6 equal rectangles.
9. Cover the filling with the other half of the rectangles. Press down around the edges to seal the filling inside. Use a fork to crimp and seal the edges further.
10. Use the fork or toothpick to poke a few holes in the top of each pastry.
11. Brush the tops of the pastries with the remaining egg wash.
12. Bake in preheated oven until puffed and golden, about 10-12 minutes.
13. Allow to cool slightly.

To make the icing:

1. In a medium bowl, whisk together the powdered sugar, cream, and vanilla extract until thick and smooth. If too thick, add a little more milk. If too thin, add a little more powdered sugar.
2. Spread or pipe the frosting over baked puff pastries.
3. Serve immediately.