Rinse the rice under cold running water in a fine sieve until the water runs clear.
Place the rice, 480 ml water, a cinnamon stick and the zest of one lemon into a heavy-based saucepan. Bring to the boil over a medium-high heat.
Reduce the heat to low, cover and simmer gently until the water has been absorbed, about 10–12 minutes.
Pour in 960 ml whole milk and stir in the caster sugar. Increase the heat to medium-low and bring back to a gentle simmer.
Turn the heat down to low and cook, stirring frequently, until the rice is tender and the mixture has thickened, about 25–35 minutes.
Remove the pan from the heat, discard the cinnamon stick and lemon zest, then stir in the vanilla extract.
Serve warm, or transfer to a bowl, allow to cool slightly, then chill in the fridge. Sprinkle with ground cinnamon just before serving.