Using sauté on your Instant Pot or a frying pan, cook the leeks until just starting to soften, then add the mushrooms. Cook until the mushrooms are soft and browned.
Add the garlic and cook for 1 more minute.
Mix the corn flour with a little vegetable stock to form a smooth slurry, then pour the cornflour mixture, remaining stock, dijon mustard and oatly cream into the sautéed vegetables and cook until thickened.
Pick the thyme from the woody stems and add this to the pie filling. Mix in the Dijon, and season to taste with salt and pepper.
Spoon the filling into a suitable size dish to fit in your Instant Vortex. We like to use an 18cm pie dish as it allows plenty of room for the air to circulate and ensure the pie cooks evenly.
Unroll your defrosted pastry, then cut a circle big enough to cover your pie. Place your pastry circle on top of your filling and crimp the edges to the pie dish to seal everything together. Poke a few small holes in the centre of the pie to allow the steam to escape, then brush the pastry with a little oat milk,
Place the pie into the basket of your air fryer.
Select Air Fry, set the time to 25 minutes and the temperature to 170°C. Cook the pie until the pastry is beautifully puffed and crisp. Once cooked, remove the pie from the Vortex and serve immediately alongside your sides of choice.