Roll the puff pastry to a big slice. Blend the fresh cheese with the mushroom mix and spread over the puff pastry. Place the beetroot over the mushrooms, add more mushrooms over the beetroot and fold the puff pastry around until it is closed. Finish and decorate with the remainings of the puff pastry and brush with egg yolk.
Put in the oven for 20 minutes until the crust is golden brown.