Step 1: Make the Tangzhong
Remove 20g of the flour and whisk it with the water in a small saucepan. Cook over low heat, stirring constantly, until it thickens and reaches 65°C/149°F. Remove from heat. Whisk in the milk, egg, and salt until smooth. Set aside.

Step 2: Prepare the Dough
In the bowl of a stand mixer, whisk together the remaining flour, sugar, and yeast. Add in the tangzhong mixture and melted butter. Stir until a rough, shaggy dough forms. Attach the dough hook and knead for 10 minutes until smooth and elastic. The dough will be slightly sticky.

Step 3: First Rise
Lightly grease a large bowl with oil spray. Shape the dough into a ball and place it in the bowl. Cover with plastic wrap and let it rise in a warm water bath for 1.5 hours, replacing the water as it cools.

Step 4: Roll and Cut the Dough
Line a 9×13-inch (22x33cm) baking dish with parchment. Divide the dough into two equal portions. Roll one half into a 20x30cm (8×12 inch) rectangle on a floured surface. Brush with the extra melted butter.

Step 5: Fold and Shape
Cut the dough rectangle in half lengthwise, then into 8 equal pieces. Fold each piece over with a small border, creating the classic Parker House fold. Repeat with the second dough half for a total of 16 rolls.

Step 6: Second Rise
Arrange the rolls in the prepared dish, seam-side down, in 4 rows of 4. Cover with plastic wrap and let rise for 45 minutes.

Step 7: Bake and Finish
Preheat oven to 180°C/350°F fan. Bake the rolls for 25 minutes until golden. Immediately brush with the remaining melted butter and sprinkle with flaked salt. Let rest 20 minutes before serving.