Pour the milk into a large saucepan and place over medium-high heat. Add in 1 teaspoon cinnamon and vanilla extract, and bring to a low boil. Turn the heat down to low and whisk in the sugar, salt and lemon zest. Ladle about a quarter-cup of the hot milk mixture very slowly into the beaten egg while continuing to whisk gently. This technique "tempers" the liquid so the eggs don't scramble. Pour the tempered egg mixture back into the saucepan and stir into the remaining hot milk. Add the rice and stir continuously over low heat until the mixture begins to thicken, about 20 minutes.
Add the butter and stir. Sprinkle lightly with remaining 1/2 teaspoon of cinnamon. Top with granola and drizzle of honey. Serve warm with milk in bowls if desired.