Slice the pumpkin (I always use Hokkaido) thinly. Rub the zest of the lemon and squeeze out the juice.
Mix the water, lemon zest and juice, cinnamon, raisins, walnuts and 60 g sugar and bring to the boil. Then add the pumpkin and simmer gently for about 10 minutes.
For the yoghurt sauce, mix the sour cream and yoghurt and sweeten with the remaining 20 g of sugar (if you like, you can add a splash of lemon juice). Serve separately with the pumpkin.