Whisk the cornstarch and water in a small bowl until smooth to create a slurry.

Combine the milk, sugar, cardamom, and turmeric in a saucepan. Bring to a boil over medium-high heat—the liquid should just begin to foam—then immediately reduce the heat to a simmer. Whisk frequently for 5 minutes to prevent the milk from boiling over or scorching on the bottom.

Reduce the heat to medium-low and whisk in the cornstarch slurry. Stir constantly until the mixture thickens to a pudding-like consistency, about 5 minutes.

Stir in the vanilla and remove from the heat. Set the pan aside to cool for about 15 minutes.

Combine the mango, banana, grapes, strawberries, oranges, apple, lychees, and blueberries in a large storage container.

Pour the custard through a fine-mesh sieve directly onto the fruit. Mix well to coat every piece, then cover and refrigerate for at least 4 hours, or ideally overnight; the fruit will release its juices and thin the custard to a silky consistency.