Preheat oven and a medium sheet pan to 425°F. On a lightly floured surface, roll thawed puff pastry into a 9 ½ x 12 inch rectangle. Cut in half lengthwise. Set aside 1 piece.
Fold the second piece in half and turn so that the folded side faces you. With a sharp knife or pizza cutter, starting 1 inch from the edge, create slits every ½ inch or so, leaving a 1 inch border at top of pastry. (Don't cut all the way through, you want to create slits that are still attached.) Unfold pastry and set aside.
(For Guava & Cheese version) In a small mixing bowl, combine cream cheese, sugar, vanilla extract and all but 1-2 tablespoons of beaten egg. Beat until smooth.
Transfer bottom sheet of pastry {the uncut piece} to a sheet of aluminum foil. For Guava & Cheese Version: Spread cream cheese mixture evenly down the center, leaving a 1 to 1 ½ inch border around the entire rectangle. Place sliced pieces of guava paste down the center.
Transfer uncut, bottom sheet of pastry to a sheet of parchment. For Guava & Cheese: Spread cream cheese mixture down center, leave a 1 to 1 ½ inch border. Place sliced pieces of guava paste down the center.
With a slightly wet finger, trace the edge of the pastry lightly to moisten dough. Carefully lift cut piece of pastry, and place on top. Press down lightly around the edges to seal. (Or use a fork to crimp.)
Combine remaining 1 ½ to 2 tablespoons of beaten egg with about a tablespoon of water. Lightly brush pastry with egg wash, and sprinkle with coarse/sanding sugar if desired.
Remove hot pan from the oven and carefully lift and arrange parchment with pastry onto pan. Bake for 15-20 minutes until pastry is puffed and golden brown.