Wash, peel, quarter, and core the apples. Cut the flesh into small pieces. Immediately drizzle with lemon juice to prevent browning.
Pour 6 tablespoons of apple juice into a small bowl. Stir the vanilla custard powder and sugar into this apple juice until smooth and lump-free.
Pour the remaining apple juice into a pot and bring to a boil over medium-high heat.
Add the cut apple pieces to the boiling apple juice. Reduce heat to medium and simmer for 2-3 minutes.
Stir in additional sugar and cinnamon to taste.
Pour the custard powder mixture into the pot while stirring constantly. Bring back to a boil over medium-high heat and cook for approximately 1 minute, stirring continuously.
Divide the warm apple mixture into dessert bowls and let cool before serving.