Preheat the oven to 180˚C. Prick each sweet potato with a fork in a few spots, then bake potatoes on a lined baking tray until very tender, about 1 hour. When cool enough to handle, scoop out the flesh, discard the skin. Purée potatoes with butter, cream, salt, and pepper in a food processor until smooth. Keep warm.
For the kale pesto:
Blanch kale leaves in a large pot of boiling salted water until bright green and wilted, about 30 seconds. Strain with a sieve and press out any excess water. Blend pistachios, olive oil, garlic, and a dash of water in a blender or food processor until very smooth.
Add kale, lemon juice and Parmesan and blitz. Add a little water as needed, until smooth.Transfer pesto to a jar and set aside.
For the miso glaze:
Combine soy sauce, vinegar, maple syrup and stock in a small saucepan.Bring to a boil over high heat. Boil for a few seconds, and then turn the heat to low and stir in miso paste. Whisk over medium heat until the miso has dissolved. Set aside.
For the mushrooms:
Heat the olive oil in a frying pan. Brush the mushrooms with the miso glaze. Fry the mushrooms, stalk-side down, on medium-high heat, pressing down now and again, until deep golden brown. Keep brushing them with the glaze. Turn, glaze and cook until tender. Season.
Glaze mushrooms again just before plating and serve on a bed of the sweet potato puree.Drizzle with kale pesto, scatter over some fresh leafy greens and finish with toasted seeds for crunch.