Add the rice and 1 cup eggnog to a medium saucepan, and place it over medium heat. Keep it just below a boil (reduce the heat if needed), and cook for 5 minutes, or until the rice has mostly absorbed the liquid.
Add the brown sugar, raisins (if using), cinnamon, and salt. Cook for another 10 minutes over low to medium-low heat, stirring often.
Add the remaining ½ cup eggnog, and simmer for another 5 to 10 minutes, or until the mixture has reached your desired thickness.
Stir in the dairy-free buttery spread. Remove the pan from the heat and stir in the vanilla.
Either serve immediately while still warm, or refrigerate and enjoy it cold.