Place the white parts of the leeks, one diced potato and a few splashes of water (you can use oil if you prefer) into a large pan over medium heat and allow to sweat for about 5 minutes. Add one cup (240 ml) of the vegetable stock, partially cover the pan and cook until the vegetables are very soft.
Meanwhile, heat a small pan over high heat and add the mushrooms (you may need to add a splash of water/oil to get them started frying). While they fry, combine ¼ cup (60 ml) warm water with the soy sauce, miso paste and vinegar in a small bowl. When the mushrooms are browned and crisp on all sides, add the liquid and fry for a few minutes more until all the liquid has evaporated. Set aside.
In a blender combine the soaked cashews with ½ cup (120 ml) water and blend until creamy. Add the cooked leeks and potatoes with their cooking liquid and an additional ½ cup (120 ml) of vegetable stock and continue blending until smooth. Be careful that your blender top doesn’t explode off from the heat.
Back in your large pan add another few splashed of water (or oil), the celery, green parts of the leeks and the thyme. Fry until soft then add the remaining two diced potatoes. When the potatoes are about halfway cooked, add the carrot. Once all the veggies are soft, add the cream base from the blender, the mushrooms, lemon juice, salt and pepper. Adjust the consistency of the chowder to your liking: adding more of the remaining stock if you would like it a bit thinner (I added an additional ½ cup/120ml).
Serve immediately with green onion or parsley sprinkled on top.