Chop the mushrooms finely and add to a frypan with the butter and fresh thyme and cook over medium heat until all excess moisture in the pan has almost disappeared. Season with salt and pepper to taste. Put aside to cool.

Preheat the oven to 190C (180C fan forced).

Roll the pastry our slightly until you can cut 2 x 21cm diameter circles (this is the size of a modern side plate usually) from the one pastry sheet. Line a baking tray with baking paper and place one of the cut pastry circles on the tray. Using a fork, prick the centre area of the pastry a number of times. Using two slices of proscuitto cover an area in the centre of the pastry circle, the size of the base of the camembert. Place half the mushroom mixture on top of the proscuitto. 

Place the camembert on top of the proscuitto and mushroom base and top with the remaining mushroom. Using the four remaining slices of proscuitto, layer them across the camembert criss crossing them and draping them down the sides of the camembert until it’s all covered.

Take the remaining circle of pastry and drape it over the proscuitto wrapped camembert and mould it around the camembert. 

Fold up the bottom sheet of pastry and twist it as you go, forming a sealed dome for the camembert.

Using the end of a knife poke a small hole in the top of the pastry dome and then run the knife down the sides of the dome forming a pattern. Brush the pastry with the lightly beaten egg yolk. 

Place in the centre of the hot oven and cook for 20 – 25 minutes or until golden brown. Slide the dome onto a serving place and allow to sit for five minutes before serving.