Activate yeast. To make the brioche dough, add the yeast, milk, and 1 tablespoon (15 g) of the sugar into a bowl and mix well. Set aside for 15 minutes, or until foamy.
Add the dry ingredients into the bowl of a stand mixer. Add the flour, remaining sugar and salt of an electric stand mixer and mix quickly.
Add wet ingredients (except the butter). Add in the eggs and vanilla, and using the dough hook, mix on low for 5 minutes, or until the dough comes together.
Add butter and knead in the mixer. Whilst the mixer is running on low speed, add the butter gradually, and once incorporated, turn the mixer up to medium speed and knead for 10 minutes. The dough should be pulling away from the sides of the bowl and have formed a “tornado” around the dough hook. Do the windowpane test on the dough by grabbing a small piece of dough in between your fingers and thumbs and stretch it out. If it tears quickly, the dough requires more kneading. If it stretches thinly and you can see the light through it, it’s perfect!
Knead by hand. Tip the dough onto a greased countertop and knead a couple of times until the dough forms a smooth ball.
Proof the dough. Place the dough ball in a greased bowl and cover with plastic wrap. Let it rise in a warm place for 1½ hours, or until doubled in size
Deflate the dough. Knock the air out of the dough by kneading it gently about 6 or 7 times until it turns into a smooth ball.