Heat the oven to 150C/fan 130C/gas 2. Butter a 1.5-litre ovenproof dish. Gently heat the sugar, milk and cream in a pan until just below simmering. Stir in the butter, rice and vanilla, then carefully tip into the baking dish.
Bake for 30 minutes then stir well and bake for another 30 minutes. Take out and stir again then return to the oven for a final 30 minutes without stirring. By this time the rice should be tender and creamy with a golden top. Serve hot with jam, if you like.