In a medium saucepan, add the rice and water. Bring to a boil over medium heat, then reduce the heat to low. Cover and let it simmer for about 10-12 minutes or until the rice is tender and has absorbed most of the water.

Add the whole milk, sugar, cinnamon, and salt to the cooked rice. Stir well and bring to a gentle simmer over medium-low heat. Cook for about 20-25 minutes, stirring occasionally, until the mixture thickens.

Stir in the vanilla extract and any optional add-ins like raisins or citrus zest. Continue to cook for another 5 minutes, stirring frequently to avoid scorching.

If using an egg, whisk it in a separate bowl. Gradually add a few spoonfuls of the hot rice mixture to the egg while whisking continuously (to temper the egg). Then, slowly pour the egg mixture back into the saucepan, stirring constantly. Cook for an additional 2-3 minutes until fully incorporated and thickened.

For an extra creamy pudding, stir in the heavy cream and butter (if using). Let the pudding cool slightly before serving.

Serve warm for a cozy treat or chill in the refrigerator for a few hours for a refreshing dessert. Garnish with extra cinnamon, fruit, or nuts if desired.