In a medium sized bowl combine your ground pork, 1/2 tsp sea salt, fennel, thyme, garlic, breadcrumbs, and melted butter.
Then, add your apple onion mixture and mix well.
Lay out each sheet of puff pastry, and cut it in half long ways so that you have four pieces.
Take 1/4 of the filling and add it to the middle of each sheet of pastry. Make sure the thickness is even, and then roll up the puff pastry into a long shape tightly and making sure there are no gaps.
Brush the egg wash along the long sides of the pastry and then roll it up. Lay the roll on the seam. Repeat with remaining puff pastry and meat mixture.
Once you have four long rolls, you can then put them in the fridge for 30 minutes to firm up. This will make them easier to cut, but this step is not necessary. Cut each long roll into 4 equal pieces. You should have 16 sausage rolls.
Add the sausage rolls to a parchment paper lined baking sheet. Use remaining egg wash to top each piece and then add sesame seeds if you would like.
Bake for 35 minutes at 350F. Some juice from the meat mixture will escape but that is normal. Serve with some honey mustard, ketchup, or eat them plain.