Rinse the dry glutinous rice in cold water 3-4 times until the water runs clear, then soak in water for 8 to 24 hours.

Drain the rice and steam it in a bamboo steamer lined with parchment paper for 20-25 minutes until translucent and tender.

In a saucepan, combine coconut milk, granulated sugar, and sea salt over medium-high heat until boiling. Lower the heat to simmer for a few minutes until smooth.

If using, stir in ube halaya or ube spread into the coconut mixture, then fold in the steamed rice and simmer for an additional 4 minutes.

In the same pan, pour in more coconut milk and sugar, bring to a boil, then add a cornstarch slurry gradually, whisking until thickened.

Slice the ripe mangoes into thin wedges. Serve the coconut rice on each plate with mango slices, drizzled with coconut sauce and sprinkled with toasted coconut.