Step 1

Put a wide frying pan over a low-medium heat and add the butter. Once melted, tip in the mushrooms and two thirds of the tarragon leaves. Increase the heat to high and cook the mushrooms until soft and golden (about 5 minutes). Season with a pinch of salt and pepper then transfer to a plate. Leave to cool, then put in the fridge to chill completely.

Step 2

Unroll the pastry sheet and cut it into 6 equal squares. Line a baking tray with baking paper and put the pastry squares on it in a single layer. Prick the pastry all over with a fork, leaving a 2cm border around the edge. Sprinkle the cheese into the centre of each square, leaving the border clear, then top with the mushrooms and sprinkle over most of the parmesan.

Step 3

Brush the exposed borders of each pastry with the egg, then put in the fridge. Heat the oven to 180°C fan/gas 6.

Step 4

Bake the pastries for 15 minutes until golden. Remove from the oven, sprinkle over the remaining tarragon leaves and a little more parmesan, then enjoy warm or at room temperature.