
Place the water in a small saucepan. Add the bread flour and whisk until you have a smooth mix with no lumps. Add the rest of the milk and whisk to combine.
Heat over medium heat while whisking constantly until the mixture thickens. The resulting mixture should have a thick, spoonable, pudding-like consistency.
Scrape the mixture into a bowl and then cover with plastic wrap. Make sure the plastic wrap is touching the surface of the tangzhong to prevent a skin from forming on top.
Allow the tangzhong to cool to room temperature, or only slightly warm (lukewarm is fine).
Activating the yeast - If you're using active dry yeast, activating it first is essential. With instant yeast, it's optional, but if you're not sure how fresh the yeast is, then I recommend activating it first to make sure.
In your mixing bowl, place the lukewarm milk and dissolve about 1 tsp / 5 g of the sugar in the liquid. Sprinkle the yeast over the milk and gently stir to mix. Allow the milk + yeast mixture to stand for about 10 - 20 minutes until the yeast is activated. The mixture should become bubbly and frothy on the surface.
Once the yeast is activated, add the milk powder (if using), the rest of the sugar, tangzhong, egg, flour, and finally the salt.
Using a spatula or the dough attachment from your mixer, mix the dough to combine the ingredients and to help form a scraggly dough.
With the dough hook attached to your mixer, knead the dough for about 5 minutes on a low speed (speed 2 or 3). The dough will be very sticky and stick to the sides, but continue mixing and the dough will start to come together.
After 5 minutes of kneading, add the butter in 3 - 4 additions, mixing for about 20 seconds in between. Scrape down the sides and the bottom of the bowl to make sure the dough mixes well.
Once all the butter is incorporated into the dough, turn up the speed to 4 - 5 (medium speed) and knead for a further 10 - 15 minutes. Scrape the bowl once or twice while kneading.
The dough should become smooth, satiny, and pull off cleanly from the sides of the bowl. To check if the dough is kneaded enough, try to lift the dough out from the bowl using the dough hook. If the dough comes off cleanly from the bowl without tearing and leaving any dough behind in the bowl - then you have kneaded the dough properly.
Place the dough on a lightly floured surface and shape it into a ball. Then place the dough back in the mixing bowl and cover with plastic wrap.
To make the salt bread on the same day, bulk ferment the dough at room temperature ONLY until doubled in size (or slightly less). This should take at least 1 hour, or up to 2 hours. I prefer to not let it proof too fast.
To make the salt bread the following day, transfer the bowl into the fridge to slow proof for 8 - 12 hours. You can keep it in the fridge for up to 24 hours hours, if needed.
Once the dough is proofed, we are ready to portion the dough and shape it into the initial "carrot-like" shapes. This can be done even when the dough is cold.
Turn the dough out onto a lightly floured surface and press all the excess air out of the dough.
Weigh the dough and divide it into 12 equal portions by weight. Keep the dough portions covered with a sheet pan or plastic wrap to prevent them from drying out.
Take a portion of the dough and roll it into a ball. Then use the palm of your hand (lightly floured if needed), and roll just one end of the dough ball back and forth to lengthen it into a carrot-like shape (see pictures in the post for reference).
Place this back under the plastic wrap. Repeat with all the dough portions so you have 12 pieces of dough that look like carrots (or stubby baseball bats!).
You can keep these dough portions covered on your countertop, OR on a sheet pan. Let them rest for about 10 - 15 minutes at room temperature. Or up to 1 hour in the fridge.
Cut the butter block into 12 equal rectangle-shaped portions. Make sure the butter blocks are no more than 1.5 - 2 inches wide. Each portion should weigh about 10 g (for less buttery rolls), or up to 15 g (for more buttery rolls).
Place the butter portions back in the fridge.
You can also use smaller butter pieces and stick them together into 12 blocks as well, instead of cutting portions precisely (so that there's no wastage).
Line two half sheet pans with parchment paper. Make sure the sheet pan has a lip around the edge to contain the melted butter.
Take one of the carrot-shaped dough portions and place it on your counter. Your work surface shouldn't be floured too much, as the narrow end of the dough should stick to the surface to help stretch out the dough.
Use a rolling pin to roll out the narrow end of the dough flat onto your work surface. Then roll out the dough in the opposite direction towards the thicker and wider end. I like to hold the wider end of the dough as I roll it out, so that I can gently stretch the dough as it's rolled out.
The resulting dough triangle should be fairly long (about 10 inches), with the wide end being no more than 2.5 inches wide (just a little wider than the butter block). This is the step that may require some practice, but it's easy once you get the hang of it!
Place a butter portion on the wide end of the triangle, and start rolling up the dough with the butter inside.
Roll up the dough towards the narrow end while making sure to center it, so that it rolls up fairly symmetrically. I like to gently stretch the dough and make it narrower as I roll it up (see pictures in the post for reference).
Then place the salt bread (with the narrow end tip on the bottom) on the parchment paper lined sheet pan. This is so that the dough won't unravel as it bakes.
Repeat with all the dough portions.
Place 6 salt breads on each half sheet pan, evenly spaced out. Loosely cover with plastic wrap or with a sheet pan cover.
Preheat the oven to 350°F / 180°C (convection oven). Place the oven rack in the middle of the oven.
Let the bread poof at around 77 - 79°F / 25 - 26°C. This can take up to 2 hours, depending on the temperature and humidity.
The salt bread will almost double in size, and will look pillowy. When you shake the tray, the bread will jiggle.
Finger indentation test to check if the bread is properly proofed.Use a finger to gently press into the dough. Since there is a piece of butter in the middle, make sure to press the dough at the ends instead of the middle. Once you've created an indentation that's about 1 cm / ½ inch deep, remove your finger and see how the indentation behaves.If the indentation bounces back completely - still under-proofed.If the indentation bounces back only partially, leaving a shallow indentation - perfectly proofed.The indentation remains and doesn't change at all - bake immediately (almost over-proofed). If the whole dough starts to deflate when poked - over-proofed.
Whisk the egg to create an egg wash. For a richer egg wash, only use the egg yolk whisked with milk / cream. You can also just brush the bread with milk or cream instead, but this will create a matte crust, while egg wash will create a shiny crust.
Once the bread is properly proofed, brush the top of the buns with the egg wash or milk wash. Then sprinkle salt flakes on top.
OPTIONAL - If you want a richer, more buttery version, you can place 1 - 3 tbsp of butter on the baking tray, so that more butter melts on the tray to make the bottoms even more crisp and buttery.
Place the bread rolls in the oven, and reduce the oven heat to 325°F / 165°C. Bake the salt bread rolls until they turn a beautiful golden color, which can take between 25 - 35 minutes. The bottom of the buns should also be a dark golden brown color.
Once baked, remove the tray from the oven. Allow the salt bread rolls to sit on the baking tray for a few minutes. There will be melted butter in the tray, but the butter rolls will absorb some of that butter as they cool.
Then transfer the salt bread onto a baking rack to cool down further.
You can serve the shio pan (classic Japanese version with less butter), or the Korean soggeum ppan (more buttery version) while still a little warm, or at room temperature.