In the bowl of a stand mixer fitted with the dough hook, add 114 grams whole milk, 3 large eggs, and 1 ¾ teaspoons instant yeast. Mix on medium speed just to break up the ingredients slightly, about 1 minute.
Turn the mixer off, then add 370 grams bread flour, 25 grams granulated white sugar, and 1 ½ teaspoons Diamond Crystal Kosher Salt. On low speed, mix until a shaggy, sticky dough forms, about 2 minutes. Increase the speed to medium, and mix for 4 - 6 minutes until the dough is quite stretchy and sticky.
With the mixer still on, begin adding 168 grams unsalted butter(cubed), one piece at a time. Use a flexible spatula to scrape down the sides of the bowl once half of the butter has been added.Add the rest of the butter until all of it has been incorporated, about 4 minutes.
Continue mixing the dough for about 8 minutes, or until the dough begins vigorously slapping the sides of the bowl. The sides of the bowl should be almost completely clean.Note: The dough may look greasy or separated at first; keep mixing until smooth and elastic.The dough should be completely homogeneous with no streaks of butter. It should be extremely soft, smooth, and tacky, and just barely sticky.
Windowpane Test: Once the dough has met the above criteria, check that it's built up enough strength via the windowpane method. Pinch off a small piece of dough, flatten it, and gently stretch it with your fingers. The dough should become thin and translucent without tearing.
Form the dough into a ball, then transfer to a large, lightly oiled mixing bowl. Cover with a towel or plastic wrap, and allow to rise in a warm environment (72°F/22°C to 75°F/24°C) for 1 ½ - 2 hours until proofed.Note: When properly proofed, the dough should pass the poke test. Coat your index finger in flour, then press your fingertip into the dough gently to make an indent; the indent should slowly fill back up halfway. If the indent springs back quickly, it needs more time.
Gently press down to deflate the dough. Then chill the dough in the fridge, covered, in the mixing bowl overnight (at least 8 hours up to 18 hours).
Form the Rolls:
Remove the chilled dough from the fridge. Divide dough into 9 equal portions. For each piece of dough, bring the corners together as if you're sealing a pouch, and seal tightly. Place seam side down on a work surface, then cup the dough in your hands, shaping it into a ball as you rotate it in a clockwise motion. Repeat with the remaining pieces of dough, and transfer each dough ball to a 8-inch by 8-inch square non-stick baking pan. Allow to proof for 45 minutes to 1 ½ hours, or until it passes the poke test again.
Meanwhile, place a rack in the center of the oven and preheat to 350°F/177°C. Just before baking, whisk 1 large egg yolk and 14 grams whole milk in a bowl until combined. Brush the tops of the buns with the egg wash and top with Flaky salt.
Bake in the oven for 20 - 25 minutes until the rolls are golden-brown on top and a thermometer inserted into the middle of a roll registers 190°F/88°C (for softer rolls, remove them from the oven at 185°F/85°C).If serving immediately, brush the tops with 28 grams unsalted butter(melted). Cool in the pan for 10 minutes and serve warm.If serving later, do not brush with butter. Cool rolls in the pan for 10 minutes, then transfer to a wire rack to cool completely. Store in an airtight container or Ziploc bag until ready to serve. Just before serving, wrap rolls in foil and warm in a 350°F oven for 10 minutes, before brushing with melted butter.
Notes
This recipe was developed using metric measurements, so while I provide a conversion to US cups, I strongly recommend using a scale.Storage: Leftover rolls can be stored at room temperature in an airtight container for 3 - 4 days. Reheating: Reheat rolls in the oven covered in foil at 350°F/177°C for 10 - 15 minutes.Variations:Instead of brushing the rolls with plain butter, try one of these two variations:
Maple Butter: Combine 2 tablespoons unsalted butter and 1 tablespoon maple syrup.
Garlic Parmesan Butter: Combine ¼ cup unsalted room temperature butter, ½ teaspoon garlic powder, 1 tablespoon minced fresh parsley, and 2 tablespoons grated Parmigiano-Reggiano cheese.