Rinse the rice until the water runs clear. Soak the rice in water for 20–30 minutes, then drain.
In a medium heavy-bottomed pot over medium heat, combine the coconut milk and cardamom. Bring the milk to a gentle simmer, then add the drained rice. Simmer, stirring occasionally so the rice does not stick to the bottom, until the milk is reduced by half and the rice is tender, about 30 minutes.
Add the sugar and stir until it dissolves. Remove the pot from the heat and stir in the rose water.
Serve the kheer topped with chopped mango and slivered almonds.