Purée the mangoes in a blender. Transfer to a pan.
Add the milk and gelatin powder. Mix.
Heat the mixture at low heat while stirring constantly. When the mix mixture starts to boil, remove from heat.
Pour the mango mixture on prepared pudding jars and let it set. (To get the slanted look, I positioned the jars in a 45-degree angle. I used a loaf pan lined with kitchen towel to position the jars steadily while the custard hardens)
On a separate pan, mix the whole milk, heavy cream, vanilla extract and gelatin powder.
Heat under low until the milk mixture starts to bubble. Remove from heat and pour over hardened mango custard jars.
Add diced mangoes as topping. You may add a layer of tapioca starch or crushed graham for added texture.
Cover the jars and chill before serving.