In a medium saucepan, bring 2 cups of water and ½ teaspoon of salt to a boil. Stir in 1 cup of medium-grain white rice, reduce the heat to low, cover, and simmer for about 15 minutes until the rice becomes tender and absorbs all the water.

Add 3 cups of whole milk, ¾ cup granulated sugar, and 1 tablespoon unsalted butter to the rice. Cook over medium heat for 15 to 20 minutes, stirring frequently until the mixture thickens into a creamy texture.

Meanwhile, in a separate mixing bowl, whisk the 3 lightly beaten eggs together with the reserved 1 cup of whole milk. To temper the eggs, slowly add a ladleful of the hot rice mixture into the egg mixture while whisking constantly.

Gradually stir the tempered egg mixture back into the saucepan with the rice mixture. Reduce the heat to low and continue cooking until the pudding achieves a velvety, smooth consistency.

Remove from heat and stir in 1 teaspoon vanilla extract, ½ teaspoon ground cinnamon, and ½ cup raisins if using. Garnish with a sprinkle of additional cinnamon and serve warm.