Prepare the caramel sauce by heating sugar in a pot until melted and amber-colored.

Carefully add water to the caramel sauce, stirring until smooth.

Pour caramel sauce into the bottom of pudding cups.

Boil water for pan steaming.

In a heat-resistant bowl, combine eggs, egg yolk, milk, granulated sugar, trehalose (or sugar), and vanilla bean seeds.

Microwave the mixture until just before boiling.

Preheat oven to 170C.

Beat eggs lightly in a bowl, avoiding foam.

Gradually pour the warmed milk mixture into the beaten eggs, stirring gently.

Strain the custard mixture through a fine-mesh strainer.

Cover the surface of the custard batter tightly with paper towels to remove bubbles.

Gently pour the custard into the caramel-lined pudding cups.

Place the pudding cups in a baking tray and fill the tray with boiling water (about 80C).

Bake on the lowest rack in the preheated oven at 160C for 30 minutes using pan steaming.

Remove from the oven and let cool slightly.

Refrigerate to chill completely.

Alternatively, bake at 170C for 23 minutes, lower to 160C for 4 minutes, then 150C for 4 minutes.