In a small pot, add water, coconut milk, agar agar powder, maple syrup, and salt. Whisk until well combined. Bring to a boil for 60 seconds while whisking. Reduce heat to low to keep warm and keep covered.
Check your mango jelly to see if it’s firm to a touch. You should be able to press it down with your thumb without any breakage. Once the mango layer is firm, pour coconut jelly liquid on the back of a spoon over your mango jelly. This ensures the hot liquid does not break the mango jelly layer as it hits the spoon first.
Cover with plastic wrap or a lid. Refrigerate for 3-4 hours until firm or overnight.
When ready to serve, use a knife to cut around the edge of the jelly to release it from the side. Tip: Insert halved toothpicks between the mold and the sides of the jelly (2 per each side) to allow air into the mold. Place a flat plate over your jelly dish. Flip upside down and the jelly should eventually slide out with gravity.
Slice into 9 squares. Optional: serve with fresh fruit and mint leaves.