For the filling
In a bowl, combine the tarragon, the gruyere and the chicken. Season with salt.
* The chicken needs to be dry and cool.
For the wrapping
Cut the filo into 30 strips, about 12 cm wide each, and lay a strip on a flat surface, with the short side of the strip close to you.
Coat the whole surface of the strip with butter using a basting brush, place a second strip on top and coat it with butter too.
Set the remaining strips aside, covered with a cloth.
Place some filling, approx. 40 gr., on the bottom part of the strip.
Lift the left corner over the filling and fold, forming a triangle. Lift again the corner that is close to you and fold again, forming again a triangle. Repeat until you have reached the end of the strip. Before the last fold, brush the remaining corner with some of the beaten egg to seal the wrap better.
Brush the pie with egg and place on a baking dish covered with parchment paper.
Repeat the process until the filling is over and you have made 15 pies.
Bake in preheated oven at about 170 degrees C for 15 minutes, until the filo is golden and crisp.
Optionally, drizzle with balsamic cream and sprinkle with extra tarragon.