Dissolve 8g of sugar into a bowl of lukewarm milk. The milk should be just warm to the touch, not hot as it will kill the yeast. Add the dry active yeast and gently mix. Allow the mixture to stand for about 5 minutes until the yeast has been activated and looks bubbly and frothy.
Combine flour, sugar and salt into the bowl of a stand mixer. Add the tangzhong and egg and mix with the dough hook attachment until incorporated.
Add the milk+yeast mixture and knead for 10 minutes.
Add the butter and continue to knead the dough for 15 minutes. The dough should be smooth, slightly sticky, and separated from the sides of the bowl.Do the windowpane test by taking a ball of dough and stretching it out slowly. If you cannot stretch it enough to see light through the dough without it ripping, continue to knead the dough for a few minutes and try again. Note: multigrain will not stretch as thin as white flour due to the gritty bits tearing into the membrane. Place the dough in an oiled bowl. Cover with plastic wrap or a clean towel and place the bowl in a warm place to proof for 45 minutes - 1 hour, or until the dough has doubled in size.
Turn the dough onto a floured surface, and split into 12 equal portions. Roll each piece into a ball. Cover with plastic wrap or a clean towel and let rest for 15 minutes.
Grease two 8" x 4" loaf pans.
Roll one portion into a 5" long rectangle. Fold the long edge into the middle, and then roll to the opposite edge. Pinch and seal the seam. Repeat for the remaining portions.
Place 6 rolls side by side, seam side down in each loaf pan. Cover with plastic wrap or a towel and let proof for 1 hour or until the dough rises to fill about 3/4 of the loaf pan.
Preheat the oven to 350°F.
Brush the tops of the dough with egg wash. Bake the loaves for 25 minutes, until the top turns golden brown and sounds hollow when knocking on it. Turn loaves onto a rack to cool.