Cook the rice in a large saucepan of boiling water for 5 minutes and drain well. Return to the pan and pour over the milk, cream, 50 g (2 oz) sugar and the vanilla extract. Cook over a medium heat for 15–20 minutes until soft and creamy. Remove from the heat and stir through the egg yolks and white chocolate until smooth.
Spoon the mixture into 4 individual heatproof ramekins and smooth over the top with the spoon. Leave to cool a little, then scatter over the remaining caster sugar. Place under a preheated hot grill and cook for 1 minute until the sugar caramelizes. Leave to cool until the surface is hard, then serve.