Soak the sultanas overnight in the rum. The next day, drain the sultanas. Set aside the sultanas and the rum.
Make the pumpkin purée. Cut the pumpkin in two horizontally and remove seeds and stringy parts. Bake in a preheated oven (170°C/gas 3) until cooked and it is beginning to collapse. Depending on the size of the pumpkin this will take about 1 hour.
Scoop the flesh out of the skin and if it is still very wet, put the pulp into a saucepan over a low heat to dry it out. This could take 15 to 45 minutes depending on the amount of water the pumpkin contains. Stir the pulp from time to time, do not let it scorch.
Blend the pulp in a food processor until smooth, then return to the pan to allow any moisture to evaporate. Allow to cool, then refrigerate until ready for use.
When you're ready to make the cake, preheat the oven to 180°C/gas 4. Butter and flour a 23cm spring-form cake tin and place a circle of floured, buttered greaseproof in the bottom of this. Combine the cherries, cranberries, dates and grated pumpkin with 1 tablespoon of flour and set aside.
Beat the remaining butter with an electric whisk until light and fluffy. Slowly beat in 400g of the sugar. Add the eggs one at a time, beating thoroughly after each addition. Fold in the pumpkin purée and spices.
Sift the remaining flour with the baking powder and salt. Combine the bicarbonate soda with the buttermilk.
Stir one third of the flour into the pumpkin and add one third of the buttermilk, repeat in the same quantities until the flour and buttermilk are used up.
Fold in the sultanas, the fruit and pumpkin mixture, the nuts and the grated peel.
. Spoon the mixture into the spring-form tin. Bake for 1½ -2 hours or until a toothpick, when inserted into the cake, comes out clean. (You may need to cover the top of the cake with foil, three-quarters of the way through the cooking time to prevent it from browning too much). Remove from oven and allow to rest for 10-15 minutes. If you are preparing the cake in advance, then at this point remove the cake from the tin, wrap in double thickness foil and store in a cake tin or other airtight container until you are ready to serve it.
. When you're ready to serve the cake, turn it out onto a cake plate. Combine the remaining sugar with the rum and or orange juice. Prick the cake all over and dribble the rum mixture over the cake while it is still warm. Allow to cool, dust with icing sugar and add a couple of sprigs of holly if you like.
. Prepare the mascarpone cream. Beat the caster sugar with the egg yolks until 'ribboning' and very pale. Fold in the brandy and then the mascarpone. Whisk the cream to soft peaks and fold into the mascarpone mixture. Serve with the pumpkin cake.
