Set out frozen puff pastry for about 20 minutes before ready to use.
Roll the pastry out to about 1/8 inch in thickness. Cut off a four inch strip and set it aside to use as decoration.
Place the Brie in the center of the puff pastry. Bring the edges of the pastry up around the cheese and crimp the edges together, sealing the cheese entirely within the pastry.
Turn the crimped side of the dough down on a greased baking sheet.
Use the remaining four inches of dough to cut out a leaf or flower design to use as a decoration. Place the design on top of the dough-covered Brie and refrigerate until ready to bake. This can be kept overnight if covered with plastic wrap.
Remove the plastic when ready to bake.
Mix the egg yolk with the water and brush the entire dough covered Brie.
Preheat the oven to 400 degrees F and bake for about 15-20 minutes. The crust should be golden brown.
Permit it to sit for about ten minutes before serving it with fresh fruit, toast points, crackers, or raw veggies.