Dissolve yeast in water and milk mixture, add sugar, salt and all flour. Mix by hand or on a slow speed of your mixing machine. No need to develop gluten. Dough can remain little lumpy. Gluten will develop by itself overnight. Cover in plastic wrap, put in the fridge until next morning.

Prepare butter for rolling. Butter has to be playable, not too soft, use parchment paper to roll it into a block, about 12-14 cm each side, transfer it to chill in the fridge for 15 minutes before rolling.

Remove the dough from the fridge. Roll it as a square, big enough to place the butter block inside. (About 25cm x 25 cm). Place butter block inside the dough, seal the edges.

Start rolling by pushing the butter from 1 side to another (lengthwise). Cut the edges. Place on top of the dough. Fold the dough as a letter. Turn the dough 90 degrees, and continue rolling lengthwise. Cut the edges, fold the dough as a letter. Cover, transfer it to the fridge for 1 hour.

Repeat the same letter folding. Cover, transfer it to the fridge for 1 hour.

Remove the dough from the fridge. Roll it in a rectangle with a narrow side about 23-26 cm. The dough should be 4-5mm thick. Cut the dough (the base of croissant has to be 8cm). Shape them and cover.

Cover croissants and let them proof for about 4-5 hours at 74-78C / 24-26C until they double in volume and become jiggly.

Egg-wash (mix one egg with 2 tbs of water). Brush croissants with egg mixture.

Preheat the oven to 375F. Bake croissants for about 25-30 minutes until golden brown.