In a non-stick pan, cook 35g of flour and 175g of water. Stir until it becomes a homogeneous paste. It needs to be at room temperature when used, so let it cool down completely. If possible, prepare this one day in advance and keep it overnight on the fridge.
If you’ve prepared your Tangzhong the day before, remove it from the fridge and let it warm up until room temperature.
Just before you start to prepare your dry ingredients, warm up 140g of milk. Don’t overdo it as it only needs to be lukewarm when used.
In a bowl, add your dry ingredients — 340g of flour, 3g of salt, 30g of sugar and, 5g of dry yeast. Mix and add your main wet ingredients — 1 medium or large egg and 140g of lukewarm milk. Mix to combine and add your Tangzhong mixture. Make sure that it is at room temperature. Finally, add 40g of unsalted butter and mix again.
Using a stand mixer at low speed, knead the dough for roughly 10 minutes or until the dough is smooth and elastic. Kneading by hand is possible and should take 15 to 20 minutes to get the same results.
Transfer the dough to a pre-oiled bowl and cover it with plastic wrap. Let it rest in a warm place for 45 minutes. You should see a significant expansion.
Add flour to your kitchen bench and rolling pin. Transfer the dough to the surface and divide it into three equal size balls. The dough should be somewhat sticky, so make use of some water on your hand if you are struggling to manipulate the dough. Working one ball at a time, use your rolling pin to stretch it in a rectangle. Fold the bottom third over the middle and the top third over the now thicker middle. Turn it 90 degrees and use your rolling pin to stretch it again. Starting at the bottom, roll it until you get an even cylinder. Do the same with the remaining two balls.
Grease a loaf pan and put your three rolls side by side and cover it with plastic wrap. Let it rest for 20 minutes.
Preheat your oven to 175c and prepare a mixture of one egg and milk. After the dough significantly rises again, brush the top with your egg and milk mixture.
Bake it for 25 minutes at 175c. You should see the dough rise and top to get evenly brown. One of the sides might slightly break but should not be too significant.
Let it cool down 15 minutes and remove it from the loaf pan. Give it 20 to 30 minutes or until it feels significantly cooler before cutting a slice.