Put dried porcini mushrooms into a bowl and cover them with freshly boiled water. Leave them to sit for a few minutes to rehydrate as you get on with your loaf.
Prepare vegetables by cleaning and roughly chopping mushrooms, peeling and roughly chopping onions and peeling and mincing or grating fresh garlic.
Heat up couple tablespoons of oil in a large non-stick pan and add onions, garlic, bay leaves together with allspice and juniper berries (if using).
Sauté them for a few minutes stirring frequently until softened and translucent but not too coloured. Next, remove allspice and juniper berries which would have already imparted their flavour onto the onions.
Add chopped mushrooms followed by dried herbs and give it all a good stir.
Sauté mushrooms and onion mixture for a few minutes until cooked down nicely. Once done take out the bay leaves.
Next, add rehydrated dried porcini together with water they've been soaking in followed by soy sauce/tamari.
Give it all a good stir and let it cook for few more minutes or until most of the liquid has evaporated, then take the pan off the heat and set it aside.
Preheat the oven to 180C/350F/Gas Mark 4.
Put cooked chestnuts into the bowl of your food processor and pulse few times to turn them into crumbs.
Add all of the remaining loaf ingredients into the bowl of food processor with chestnuts and puree until you get smooth paste. You might need to do it in batches depending on the size of your food processor. You might also need to stop pureeing couple of times to scrape mixture from the sides of the bowl and puree again for nice and smooth finish (although it doesn't need to be a perfect puree). Transfer seasoned loaf mixture to a large bowl, taste and season with salt and pepper. Also feel free to adjust other seasoning.
Transfer pureed mixture into prepared, lightly oiled loaf tin lined with baking paper overlapping on both sides for easy loaf removal later.
Press mixture nice and tight using large spoon to help you.
Bake in preheated oven for approximately 45 minutes until nicely browned and firm to touch.
Let the roast cool in the tin for a few minutes before removing it onto a board.
Serve and enjoy!