Unroll the sheet of puff pastry and cut it into two equal-sized pieces.
Roll each piece out into a square on a floured surface. Cover in food wrap and refridgerate.
How to make the mushroom filling
Finely dice the shallot and garlic, and cut the fresh mushrooms into small squares. Rehydrate the dried porcini mushrooms and blot them with kitchen paper before slicing them very finely.
Heat oil in a pan or skillet and saute the shallot for 1-2 minutes before adding the garlic and fresh mushrooms, then add the porcini mushrooms.
Cook until all the moisture has evaporated, then transfer to a bowl and allow them to cool down to room temperature.
Stir through the beaten egg (reserving 1 tablespoon for egg wash) and truffle oil. Refrigerate until needed.
How to make your pinwheels
Spread the mushroom filling over the sheets of puff pastry, leaving a small margin at the top and bottom. Eggwash those areas with the remaining beaten egg using a pastry brush.
Grate parmesan over the surface, and season with salt and pepper.
Roll the puff pastry inwards into a tight log, then wrap it in plastic food wrap and refrigerate for at least 20 minutes.
Slice pinwheels into small rounds around 1cm thick and lay on a lined baking tray. Cover and refrigerate whilst the oven preheats.
Preheat the oven to 200C/400F.
Eggwash the pinwheels and bake for 15-20 minutes until golden brown and crispy.
Notes
It is very important to cook out all of the water in the mushrooms, or the truffle porcini mushroom puff pastry pinwheels will be soggy.You can pulse the mushroom filling in a food processor to blend it down finer into a paste, but I find that as long as you cut the mushrooms small enough and use the egg to help bind the filling, it stays put just fine.If baking these pinwheels straight away, place the puff pastry rolls in the freezer to chill them down quickly whilst preheating the oven. The colder they are, the easier they are to slice up.It can help to use a serrated knife to slice up the puff pastry roll.Always preheat the oven. Puff pastry needs a hot oven to cook properly.