Mix the flour, currants, raisins, breadcrumbs, sugar, suet, mixed spice, cinnamon and nutmeg together in a large bowl.
Add the plums and apple pieces.
Add the orange zest and juice, the rum and the eggs and mix well.
Gradually add milk, stirring constantly, until the mixture will drop from the spoon when pulled from the bowl (dropping consistency).
Place the plum mixture into the pudding basin and cover with greaseproof paper or a pudding cloth. Secure the paper or cloth with kitchen string.
Using a pan with a lid large enough to comfortably contain the pudding basin, half-fill the pan with boiling water. Add the pudding basin and cover with the lid. Steam the pudding for three hours. Replenish the water level if necessary.
Remove the basin from the pan and allow to cool slightly.
For the sauce, whisk the egg for five minutes until light and foaming.
Add the sugar, butter and vanilla seeds and whisk well.
Carefully fold in the whipped cream until well combined.
To serve, spoon out the plum pudding onto plates and spoon the sauce alongside.