In a large bowl, combine the brown sugar and salt. Set aside.
Brown the butter in a skillet and pour it over the sugar mixture.
Let the skillet cool.
To make the tangzhong use the same skillet and combine the milk with 3 tablespoons (23g) of the bread flour.
Whisk until smooth with no lumps.
Place the skillet on low heat and cook while stirring. Start with a whisk then switch to a rubber spatula. You want it thickened, like paste. It will form one clump in 2 to 3 minutes.
Remove from the heat and add it to the bowl, whisking smooth.
Add the eggs and vanilla and continue whisking until smooth.
Add the remaining 2 1/2 cups plus 1 tablespoon (307g) bread flour and the baking powder and baking soda.
Use a spatula to stir until well combined.
Chill bowl 15 mins before adding chocolate so it doesn't melt.
Chop the milk chocolate into coarse pieces.
Remove the dough from the fridge and add chocolate.
Chill 1 hour then scoop into 50 gram mounds.
Chill covered in fridge 24-48 hours.
Bake 14-15 mins at 350.
