To prepare your custard, mix the custard powder (corn-starch flour) with milk, until well combined. Transfer to a small pot and bring it to a boil. Cook custard in medium heat, and stir constantly. Continue stirring for about 10 - 15 minutes. When it starts to boil, turn off the heat and let it cool down.
Start with hibiscus flowers. Place hibiscus flowers in a medium cup and pour hot water in and let dissolve their colour. When water gets temperature 60°C, pour gelatine powder and stir well. When gelatine still doesn't dissolves well, cook on low heat for few minutes until dissolved well. Let the gelatine cool down and set aside.