In a small saucepan over a medium/low heat, add your vegan butter and allow it to melt. Add the grated onion and cook for around 5-7 minutes or until it is nicely caramelised.

Add the flour and allow to cook for a further 30 seconds, stirring constantly. Gradually add the oat milk a few tablespoon at a time. Stir to combine and cook for a further minute to thicken. Season and stir in the dijon. Cover the pan and set aside.

In a small frying pan over medium heat, add the sliced onion along with a drizzle of olive oil. Cook for around 5 mins until nicely browned and caramelised. Remove from the pan and set aside.

Now add the two halves of shimeji mushrooms to the pan with another drizzle of olive oil. Using a smaller cast iron pan or a heavy pan lid, press down on the shimeji until they sizzle loudly (this helps to sear them and turn them nice and brown). Leave the cast iron pan/lid where it is and allow to cook for around 5 minutes. Remove the lid and add the soy sauce. Flip the mushrooms carefully, making sure not to break up the “steak”. Repeat the searing process on the other side for a further 5 minutes.

Spread a layer of the soubaise on both sides of the toasted sourdough. Top with the onions, followed by the mushrooms and then the baby bok choi. Season, slice and eat!