Chicken (Quorn) Pie with Wholegrain Mustard

- A bunch of spring onions/scallions
- 1 heaped tablespoon of flour (additional if you wish to thicken the sauce)
- 150g Button Mushrooms (optional - I used frozen peas)
- 2 teaspoons of Wholegrain Mustard (or English)
- 1 heaped tablespoon of Creme Fraiche
- 500ml of Vegetable stock (chicken if you're not using Quorn)
- A few sprigs of Thyme (I used dried)
- 1/2 tsp of ground nutmeg (I grated about 1/3 of a whole one)
- 1 sheet of pre-rolled shortcrust pastry (the recipe calls for puff, but it's your choice)
- 1 egg