In a large mixing bowl, combine the all-purpose flour, sugar, and active yeast. Gradually pour in warm milk and melted butter, stirring until just combined. Add beaten eggs and vanilla extract, mixing until smooth. Knead the dough on a floured surface for about 8-10 minutes until it becomes elastic and feels silky to the touch.

Transfer the kneaded dough into a greased bowl, turning it to coat evenly. Cover with a clean kitchen towel or plastic wrap and let it rise in a warm place for about 1 hour, or until it has doubled in size.

While the dough is rising, prepare the custard filling. In a medium saucepan, mix custard powder and sugar with water, stirring over medium heat. Cook, constantly stirring, until the mixture thickens and bubbles for about 5-7 minutes. Remove from heat and let it cool slightly before using.

Once the dough has risen, gently punch it down to release air. On a lightly floured surface, roll out the dough into a rectangle. Cut the dough into equal pieces and place a generous spoonful of the custard filling in the center of each piece. Fold the dough over to encase the filling and shape them into rolls.

Place the shaped rolls seam side down on a baking sheet lined with parchment paper. Cover them with a kitchen towel and let them rise for another 30 minutes.

Preheat your oven to 375°F (190°C). Once the rolls have risen, bake them in the preheated oven for 20-25 minutes or until golden brown.

After baking, remove the Custard-Filled Sweet Bread from the oven and let them cool on a wire rack. Allow them to cool completely before serving.