Butter a 1 litre pudding basin.
Mix flour, currants, raisins, breadcrumbs, sugar, suet, mixed spice, cinnamon, and nutmeg in a large bowl.
Stir in the chopped plums and apple pieces.
Add orange zest, orange juice, rum, and eggs, then mix well.
Gradually stir in milk until the mixture reaches a dropping consistency.
Transfer the mixture to the basin and secure with greaseproof paper or a cloth and string.
Steam the pudding in a covered pan of boiling water for three hours.
Remove from the pan and let cool slightly.
Whisk one egg for five minutes until light and foaming.
Add icing sugar, melted butter, and vanilla seeds and whisk thoroughly.
Fold in the whipped cream until combined.
Spoon the pudding onto plates and serve with the sauce.