Slice chicken breast. Wash and slice mushrooms. Peel and slice onions.
Heat a dash of olive oil in a non-sticky pan.
Fry chicken on each side. Add onions and mushrooms. Cook 5 minutes stirring regularly.
Pour white wine and let it evaporate.
Add cream, mustard, pepper, salt, parsley, thyme and grated cheese.
Add egg and mix very quickly. Remove from the heat and reserve.
Preheat oven to 200°C (400°F).
Put first puff pastry on your pie dish. Prick with a fork. Pour mixture.
Place second puff pastry on top and close the pie.
Mix egg yolk with 2 tablespoons of water. Brush on top of the pie.
Bake for 25 to 30 minutes.