Finely chop the leeks.
In a pan melt the butter then add chopped leeks, salt, pepper, thyme and a pinch of nutmeg, fry for a few minutes then turn on low heat and simmer for 10-15 minutes until soft.
Slighly warm the plantbased milk.
Preheat the oven at 180°C (350°F).
As soon as the leek and onions are soft sprinkle them with the flour, stir well and cook for a couple of minutes. Gradually add the warmed milk stirring constantly. Cook the mixture for a bunch of more minutes until it thickens, then add the nutritional yeast (or vegan cheese previously grated or finely chopped). Stir until the cheese has melted, then add the fresh spinach and give it a last stir. Set aside.
Roll the pastry and coat the bottom of a round 24 cm tin (or 24x204cm squared).
Pour the filling over the pastry then cover with a second layer of puff pastry, making sure to seal all edges.
Decorate as you please and place it in the fridge for a few minutes (ideally 30, but 10 will do as well if you’re in rush. Alternatively you can make the pie the day before and store it in the frige before baking it).
Bake for 25-30 minutes and enjoy with your favourite sides!