Preheat the oven to 180C/160C fan. Cut a lid in the top of the pumpkin and scoop out all of the insides. Put it onto a baking tray and put into the oven, with its lid on, for 20 minutes to heat through.
Whisk together the sugar and melted butter, then add the egg and vanilla. Mix together then fold in the flour, spices, milk and dates. Mix until just combined then tip it into the warm pumpkin.
To make the sauce, sprinkle the muscadavo sugar over the top of the uncooked cake mixture. Dot the butter on top of this, then pour over the boiling water. Leave the pumpkin lid off this time and bake for 1 hour, until the cake is risen and firm to the touch. Serve immediately by taking big spoonfuls out from the top and revealing the sauce below.