1Make the Tangzhong: In a saucepan, combine ½ cup whole milk, ½ cup water, and ¼ cup bread flour. Cook over medium heat, whisking constantly, until a paste forms. Let it cool.
2In a large bowl, combine 4 ½ cups bread flour, 2 teaspoons kosher salt, and 2 tablespoons sugar.
3In a separate bowl, whisk together 1 whole egg, 1 egg yolk, and the yeast mixture.
4Add the wet ingredients to the dry ingredients in the mixer bowl. Add ¼ cup room temperature unsalted butter. Knead on low speed for 10 minutes until the dough is sticky.
5Lightly oil a large bowl. Transfer the dough into the bowl and cover with plastic wrap. Let the dough proof until doubled in size (1 to 1 ½ hours).
6Lightly grease a large baking dish with oil. Punch down the doubled dough and divide it into 18 pieces. Shape each piece into a small ball and arrange them in the prepared baking dish.
7Cover the baking dish with a clean kitchen towel and let the rolls double proof for 1 hour.
8Preheat oven to 375°F (190°C). Brush the rolls with egg wash.
9Bake for about 20 minutes, or until golden brown.
10While still hot, brush the rolls with melted unsalted butter and sprinkle with Maldon salt.