Put the small white mushrooms in a saucepan with a lid.
Add the lemon juice and margarine, season with pepper and salt, and let it simmer for 5 minutes with the lid on.
Place the oyster mushrooms on a baking sheet lined with parchment paper with the flat side down, season generously with pepper and salt, sprinkle the satay spices over, drizzle the oil on top, and bake for 20 minutes at 200°C until nicely colored.
In a large pot, melt the margarine, let it foam, and add the flour all at once, mix well and let it cook for 2-3 minutes until it smells like cookies and to eliminate the flour taste.
Pour in all the milk, stir vigorously to remove all lumps, add the broth and cream, and let it come to a brief boil, then add the small mushrooms and the baked oyster mushrooms as well as the vegan meatballs, and let everything simmer on low heat for a while longer.
Taste and season with pepper and salt, if it’s too thick, you can add extra broth.
Roll out the puff pastry, cut into triangles, brush with some oil, and bake them in the oven for 25 to 30 minutes until crispy and golden brown.
Serve with the vol-au-vent along with some crispy fries and puff pastry on the side.