Bring the rice, butter and water to the boil in a large saucepan over high heat. Reduce heat to medium-low, cover and simmer until the rice is tender and the liquid has been absorbed, 20 to 25 minutes.
Whisk together 475ml milk, flour, sugar, egg and vanilla extract in a bowl and pour the milk mixture over the cooked rice. Stir to combine, and simmer over low heat for 15 minutes.
Stir in 250ml full fat milk, cream, raisins and cinnamon until thoroughly mixed then allow to cool for a few minutes. Serve warm or cold.