In the bowl of your stand mixer fitted with the dough hook, combine the flours (reserving ½ cup from any of the flours to add in later), sugar, yeast and salt. Once mixed, pour in all the wet ingredients except the olive oil and knead on medium speed for 3-5 minutes or until a smooth dough has formed. This can also be kneaded by hand.
Pour in about half of the olive oil into the bowl and knead until mostly incorporated. (don't add in all the olive oil at once as it could easily spill out from the bowl). Add in the reserved ½ cup flour and continue to knead. Lastly, pour in the remaining olive oil and knead until a smooth glossy (but no longer oily) dough has formed. This whole kneading process will take 20-30 minutes. It will look like a lot of oil at first but with patience it will be incorporated and make the best enriched bread. Test dough by doing the window pane test*
Place the dough ball into a large lightly greased bowl, cover with a towel or plastic wrap and rest in the refrigerator overnight.
The next day, line a 9x5" loaf pan with parchment paper with a bit of overhang and set aside.
Dust your work surface with flour, punch your cold dough and begin shaping. There are many ways to shape brioche but the following is my preferred method: Divide the dough into 6 equal parts. Grab one piece then using your fingertips nudge the dough into a rough rectangular shape. Grab one end and fold up and over to meet the middle. Repeat with the other end of the rectangle to form a business letter fold. Give it a 90° turn and shape again to a rough rectangle. Starting from one end of the rectangle, tightly roll the dough like a jelly roll. Repeat this process with the other 5 pieces then squidge them into the prepared pan. Loosely cover with a towel and let rise for 1-2 hours or until double in size.
Lil tip: You'll know when you're bread is ready for the oven when you gently press a part of the dough and it springs back slowly and leaves a small indent. If it springs back quickly, it's not yet ready. If the dough deflates, then it's overproofed. You'll need to take it out and reshape it.
When your bread is almost done, preheat your oven to 350°F (180°C). Combine all the ingredients for the milk glaze in a small bowl. Brush the glaze over the bread and bake for 20 minutes. Take the bread out, lower the temperature to 320°F (160°C) and brush a second coat of the milk glaze. Leave to bake for 25-30 minutes or when a skewer inserted at the center comes out clean. Let the bread cool for 10 minutes then remove from the loaf pan to cool on a wire rack. Once bread has fully cooled, slice and enjoy!