Set the oven at 200 c, 180 Fan , Gas 6. Peel the butternut, halve it lengthways and discard the seeds or fibres. Cut the flesh into large chunks then place in a single layer in a roasting tin.
Peel the shallots and halve them, then tuck among the squash.
Mix the olive oil and the paprikas, then spoon over the squash and turn to coat. Put into the oven and bake for about an hour or until the squash is patchily browned but thoroughly soft and tender. Do keep an eye on it so it doesnt burn.
Warm the vegetable stock in a large saucepan. Add the squash and shallots to the stock and place over a moderate heat, season with a little salt and pepper and bring to the boil.
Partially cover the pan with a lid and simmer for 20 minutes, until the squash is falling to pieces. Crush a few pieces of the squash into the liquid to thicken it slightly.
Slice the mushrooms thinly, then fry them in the olive oil in a shallow pan until golden. Peel the ginger and shred it into very fine matchsticks. Add to the mushrooms and cook for a minute or two. When all is golden sizzling remove from the heat.
Ladle the soup into deep bowls, then spoon over the soured cream, mushrooms and ginger.