Heat the oven to its highest setting 240C (220C fan). In a large, high-sided baking tray, whisk 100g of the butter with the miso and water, then lay in the pumpkin pieces and cover with foil. Bake for 35 minutes, remove the foil, then bake for another 30 minutes, until the pumpkin is completely soft, and remove.
Turn down the oven to 200C (180C fan)/. When the pumpkin is cool enough to handle, remove the skin and put all the flesh and the reduced miso butter liquid from the tray in a blender with the milk, parmesan, half a teaspoon of salt, plenty of pepper and the remaining 50g butter, and blitz on high speed until completely smooth.
Grease and line a 23cm spring-form cake tin, then arrange the pappardelle nests inside it. Pour the pumpkin sauce over the top, and tap the tin on a work surface to level out the surface and ensure the pasta is completely covered in the sauce (you shouldn’t have any dry areas of pasta visible). Cover the tin with foil and bake for 45 minutes. Remove the foil, drizzle three tablespoons of oil over the top and bake for 20 minutes more, rotating the tin once halfway, until the pasta is crisp on top and cooked all the way through. Leave to cool for 20 minutes before releasing the pie from its tin.
While the pie is baking, mix all the ingredients for the tomato salsa with a quarter-teaspoon of salt.
Drizzle the cream and remaining tablespoon of oil over the top of the pasta pie, sprinkle over the parsley and serve with the tomato salsa alongside.