Preheat the oven to 180C.
Finely slice all the vegetables and place together in a bowl. Add a drizzle of oil with the tomato paste and toss with hands to coat the vegetables evenly.
Transfer to a baking tray and roast for 30-40 minutes until vegetables are caramelised.
Once vegetables are caramelised, remove from the oven and add in water (or vegetable stock) and scrape the tray to remove any bits that are stuck.
Transfer to a pot and add in kombu, thyme and peppercorns then simmer on low heat for 25-30minutes.
Strain the liquid through a fine strainer, season with salt and balsamic vinegar as needed.
Once strained, blend in xanthan gum until mixture is glossy and lightly thickened.
Cut mixed mushrooms to thick 3cm slices and then place butter in a large frying pan with the mushrooms. Cook until mushrooms are golden brown on both sides.
Add in the garlic and toss in the pan until fragrant, then add in thyme and red wine. Cook out the red wine until it has almost evaporated.
Deglaze with stock and continue to cook further until stock is almost evaporated.
Turn off the heat and add in vegetable jus, toss in the pan until mushrooms are coated with the jus.
Brown butter (Place unsalted butter in a pot and cook over low heat until butter has caramelised and browns, cool and strain).
Place cream in a pot and reduce by one third over low heat then in a blender put all the ingredients in and blend until smooth. Season with salt.
In a bowl place a large spoonful of potato purée in the middle and then the braised mushrooms next to it, season with salt and chopped parsley.
Garnish with pickled onions. Serve immediately.