1: To make the plum sauce, melt the butter in a saucepan over a medium heat. Add the sugar and cinnamon stick and stir until the sugar dissolves. Add the plums and lemon juice, turn the heat to low and continue stirring until the plums break down into a purée, which will take about 20 minutes.
2: Remove the cinnamon stick, then pour the purée into a blender and blend until smooth. Pass the sauce through a fine sieve into a bowl, then leave on one side until needed.
3: To make the Christmas pudding ice cream, put the cream and milk into a saucepan over a high heat and bring to the boil. Whisk together the sugar and egg yolks in a heatproof bowl until fluffy and pale. Pour the boiling cream on to the egg mix, whisking. Pour the mix back into the pan and simmer, whisking, until the custard reaches 82°C on an instant-read thermometer.
4: Pass the hot custard through a fine sieve into a bowl. Stir in the glycerine, if you are using, and whisk together. It acts as an anti-freeze and helps the ice cream stay smooth and ice-crystal free. Leave to one side to cool completely.
5: Place the Christmas pudding in another bowl. When the custard is cool, stir it into the Christmas pudding, then pour into an ice cream machine and follow the manufacturer’s instructions. Place in a freezer-proof container and freeze for up to 3 months.
6: To make the cake, place the unpeeled oranges and water to cover in a saucepan over a high heat and bring to the boil. Turn the heat down to low and leave the oranges to simmer for 2 hours, or until very soft and tender. Drain the oranges and leave to one side. Preheat the oven to 180°C/Gas Mark 4 and grease a 24cm loaf tin with butter and line the base with baking parchment.
7: When the oranges are cool enough to handle, cut each in half and remove the seeds. Place everything but the seeds – peel, pith, fruit and all – in a food processor and process until finely chopped. Weigh out 450g of the chopped oranges and discard the remainder.
8: Return the 450g chopped orange to the food processor and add the ground almonds, sugar, eggs, baking powder, ground cinnamon and ground ginger and process again until well mixed. Pour the batter into the tin.
9: Place the tin in the oven and bake the cake for 1 hour, or until the cake is set and it comes away from the side of the tin. It is a moist cake, so you can’t test it with a skewer. You’ll probably have to cover the top of the cake with kitchen foil, shiny side down, after about 40 minutes to stop it from burning.
10: Remove the tin from the oven and leave the cake to cool completely in the tin on a wire rack. When the cake’s cool you can take it out of the tin and peel off the paper. Wrap the cake in kitchen foil and store in an airtight container for up to 3 days.
11: When you’re ready to serve, take the ice cream out of the freezer about 10 minutes in advance to soften just a bit and reheat the plum sauce gently. Dust the cake with icing sugar and slice, then serve with the plum sauce and Christmas pudding ice cream on the side and sliced peeled oranges for decoration.