Place sticky rice in a large bowl and cover with cold water by at least 2 inches. Let it soak at room temperature for a minimum of 4 hours or overnight.
Rinse the rice under cold water until it runs clear after draining.
Prepare a steamer with cheesecloth-lined bamboo steamer or a heatproof bowl over a pot of simmering water with a few inches of water in the pot.
Add soaked and drained rice to the steamer or bowl and steam for 30 minutes until cooked through.
Prepare the mangoes by selecting ripe ones, trimming the stems, and slicing them thinly.
For the final drizzle, combine the coconut cream with a pinch of salt and heat over low heat to create a creamy sauce.
Assemble the brownie by placing the steamed rice into a serving dish, topping with mango slices, and drizzling with the warm coconut sauce. Garnish with toasted sesame seeds or salt flakes if desired.