In a large pot over medium-high heat, bring the rice and water to a boil. Lower heat to a heavy simmer and, stirring occasionally until water has absorbed. This step usually takes about 10 minutes.
Add the sugar, vanilla bean seeds or extract, and ground cardamom. Stir a few times to incorporate.
Bring heat back up to medium (medium-low if you are using a gas range). Add milk 1/3 of a cup at a time. We recommend stirring constantly, which ensures you don't scorch the milk. It takes about 5 minutes for each cup of milk to thicken and about 45 minutes in total to get all of the milk incorporated into the porridge.
Once all of the milk is incorporated and there is no longer any liquid in the pot, spoon the porridge into 2-4 bowls. Sprinkle each serving with a 1/2 teaspoon of ground cinnamon and put a 1 tablespoon sized dab of butter atop the cinnamon. Serve with fresh, frozen or dried fruit.