Cost per Serving:
Preheat oven to 375°F. Grease a shallow 2 1/2-quart baking dish.
In a medium saucepan, bring 1 3/4 cups water to a boil. Stir in rice, cover, reduce heat and simmer until all water is absorbed, 20 to 25 minutes. Remove from heat.
In a small saucepan, during last 5 minutes of cooking rice, bring coconut milk, sugar and salt to a boil over medium-high heat. Cook for 4 minutes. Turn off heat and stir in rum.
Fluff rice with a fork. Pour coconut milk on top. Cover with wax paper; let rest for 30 minutes.
Meanwhile, spread coconut in a single layer on a baking sheet and toast in oven, stirring frequently, until golden brown, 7 to 10 minutes. Let cool. (Coconut can be toasted up to 1 week ahead; store airtight.)
Serve rice pudding at room temperature or warmed slightly on stove top, topped with a sprinkling of mango and toasted coconut.