Slice the onion and mushrooms. Preheat the oven to 200C. Put the mushrooms into a bowl, drizzle 1tbs olive oil and rub it generally, careful not to break them. Spread the mushrooms in a single layer on a baking tray. Bake for 5, 7 minutes.
Heat the rest of the oil in a heavy bottom pan. Saut� the onions until soft and translucent. Add balsamic vinegar, season it with salt and pepper and saut� on a very low heat until the onions are caramelized. Careful not to fry it or brown it. You should have a couple of tablespoons of finished product.
Add truffle oil to the cashew cream and add seasoning if needed.
Toast the bread and spread it with cashew cream, divide the caramelized onions between the two toasts. Pile baked mushrooms over the onions, season it with sea salt if needed, serve it warm with some greens on the side.
