Set the oven at 200°C/ Gas 6. Peel the butternut, halve it lengthways and discard the seeds and fibres. Cut the flesh into large chunks, then place in a single layer on a baking sheet or roasting tin. Peel the shallots, halve them, then tuck them among the squash.
Mix the olive oil and the paprikas, then spoon over the squash, slide the dish into the oven and bake for about an hour, or until the squash is patchily browned but thoroughly soft and tender.
Warm the vegetable stock in a large saucepan. Add the squash and shallots to the stock, place over a moderate heat (use a few spoonfuls of stock to deglaze the roasting tin if there are any interesting bits of roasted squash and shallot left), then season with salt and a little pepper and bring to the boil. Partially cover the pan with a lid and simmer for twenty minutes, until the squash is falling to pieces. Crush a few pieces of the squash into the liquid with a fork to thicken it slightly.
Slice the mushrooms thinly, then fry them in the olive oil in a shallow pan till golden. Peel the ginger and shred it into very fine matchsticks, then add it to the mushrooms and continue cooking for a minute or two. When all is golden and sizzling, remove from the heat.
Ladle the soup into deep bowls, then spoon over the soured cream and the mushrooms and ginger.
