Begin by greasing a mixing bowl with some butter or flavorless oil and setting this aside.
Sprinkle the dry active yeast and 1 teaspoon of the sugar into your warmed milk. Stir this and set aside for about 10 minutes to allow the yeast to activate.
Meanwhile, in the bowl of a stand mixer fitted with a dough hook, stir together your flours, remaining sugar and salt.
When the yeast is ready, add this to the flour mixture, immediately followed by two whole eggs and one egg white. Reserve the remaining yolk for an egg wash when baking.
Knead the dough with the mixer on a low setting for about 15 minutes until it has formed a sticky dough that is showing signs of pulling itself away from the sides of the bowl.
After 15 minutes, with the mixer still on a low setting, add your butter a couple of small bits at a time.
Once these have all been added, continue kneading for another 15 minutes still on a low setting, until the dough is again pulling itself from the sides of the bowl.