This quick dessert is one of my all-time favorites. We have it at the local Thai restaurant but it is pretty easy to duplicate at home. It can be made ahead and assembled at the last minute. Keep the ingredients in the fridge and don't peel the mango until you are ready to use it or it will turn brown.
In a saucepan, combine 1 cup short grain rice in 2 1/2 cups water with 1 t butter. Bring to a boil then cover. Reduce heat to low and cook for 20 minutes. Cool rice. In a small saucepan, bring one can of coconut milk and 1/2 cup granulated sugar to a boil. Cook for 30 seconds, stirring continuously. Remove from heat and cool completely. Peel one mango and slice or dice.
To serve, scoop rice into a shallow dish. Arrange slices of mango on top. Drizzle (or drench) with coconut mixture. Serve immediately.