Parmesan or Pecorino Romano cheesegrated (optional)
Preheat oven to 400 degrees. Line 2 cookie sheets with parchment paper or silicone mats.
Unfold thawed puff pastry sheets.
Cut sheets along fold then each rectangle into thirds to make 9 squares from each sheet. I use a pizza cutter which works extremely well.
Spread about ¼ teaspoon mustard on each square of puff pastry. You can put on more or less depending on your tastes.
Place a little fontina cheese on top of mustard, followed by a half slice of apple. I used a mandolin to slice mine as it slices it evenly and the perfect thickness.
Sprinkle with bacon bits (about ½ slice of bacon per bundle) and top with shredded mozzarella cheese.
Note: Make sure that the bundles are not overfilled as it will cause the puff pastry to open and lay flat when baked.
Whisk egg with about 1 Tablespoon of water to use as an egg wash. This will also aid in keeping the bundle together.
Bring 2 opposite sides of bundle up over top on filling, dab with a little egg wash and press them together. I bring the edges that are opposite from the points of the apple. Continue with remaining bundles.
Move bundles to prepared baking sheets. I usually put 9 on each sheet.
Brush all the bundles with more egg wash. This will create a nice glossy brown finish once baked. Sprinkle with grated Parmesan, if desired.
Place in oven and bake for 15-18 minutes.
Remove from oven and cool 5 minutes before plating the appetizers for guests.