Add the rice and water to a pot over medium high heat. Cover, reduce the heat to medium-low and boil for 15-18 minutes, or until the rice is cooked completely.
Stir in 3 ½ cups of milk, sugar, salt and raisins if using into the pot with the rice. Reduce the heat to low and simmer for 15-20 minutes until thickened and creamy.
In a mixing bowl, whisk together the eggs and ½ cup of remaining milk until well combined.
Add a small amount of the hot rice mixture to the bowl with the eggs, and stir constantly to temper it.
Once tempered, pour the egg mixture into the pot with the rice. Simmer for 2-3 minutes.
Remove the pot from the heat, and stir in the vanilla, cinnamon and butter before serving.