Preheat the oven to 180C/350F/Gas 4.
Pour the milk, cream and vanilla into a pan and boil for a minute. Remove from the heat and set aside to cool.
Tip the eggs and sugar into a bowl and beat together until light and fluffy. Fold the flour into the mixture, a little at a time.
Pour the cooled milk and cream onto the egg and sugar mixture, whisking lightly. Set aside.
Place a little butter into an ovenproof dish and heat in the oven until foaming. Add the plums and brown sugar and bake for 5 minutes, then pour the batter into the dish and scatter with flaked almonds, if using.
Cook in the oven for about 30 minutes, until golden-brown and set but still light and soft inside.
Dust with icing sugar and serve immediately with cream.