In a saucepan, whisk together 35 gm flour and 168 gm water until smooth. Cook over medium-low heat, stirring constantly, until the mixture thickens into a pudding-like consistency. Remove from heat and transfer to a clean bowl to cool to room temperature. Use immediately or store in the fridge for up to a few days; if chilled, bring back to room temperature before use.

In the bowl of a stand mixer, combine 320 gm flour, 7 gm instant yeast, 43 gm sugar, 16 gm milk powder, 2 gm salt, 100 gm milk, and the cooled tangzhong. Mix and knead for 3 to 5 minutes until the dough comes together.

Add 33 gm butter to the dough and knead on medium speed for an additional 12 to 14 minutes until the dough reaches the windowpane stage — stretchable and thin without tearing. If the dough feels too dry, add milk one tablespoon at a time.

Place the dough in a large greased bowl, cover with cling film or a damp cloth, and let it rise in a warm place for about 1 hour or until doubled in size.

Turn the dough onto a lightly floured surface. Gently flatten it and use a bench scraper to cut into 12 equal portions, being careful not to over-handle. Shape each portion into smooth balls.

Place the dough balls onto lined baking trays about 5 cm apart. Flatten each ball with your palm to about 2 cm thick and 8 cm diameter. Use the back of a glass to press a 4 cm wide indent in the center, leaving a 2 cm border around the edge.

Whisk chilled vanilla custard or pastry cream to loosen it, then spoon into the indent of each bun. Avoid overfilling to prevent overflow during baking. Brush the edges of each bun with milk.

Allow the buns to rest at room temperature for 30 minutes to puff up slightly.

Preheat the oven to 180ºC (356ºF). Bake the buns on the middle rack for 20 minutes until golden brown and cooked through.

Remove buns from the oven and immediately brush the tops with 10 gm melted butter. Transfer to a wire rack to cool before serving.