Mix together dry ingredients: flour, salt, sugar, and yeast
Shave cold unsalted butter into the flour using a vegetable peeler, coating slices with flour as you go
Add cold water and cold milk mixture to the dry ingredients
Mix until no dry flour remains and let dough rest in fridge for at least one hour
Roughly shape dough into a rectangle and divide in half
Roll out each half and perform four sets of trifolds, using generous flour on the cutting board
Cover each half with plastic wrap and refrigerate for about 24 hours
Divide each half into quarters and work with one quarter at a time
Roll out into a rectangle and cut into two triangles for large croissants
Proof at room temperature for 4-5 hours until doubled in volume, or freeze on tray for at least one hour and transfer to plastic bag
For frozen croissants, place on parchment-lined baking sheet and let defrost and rise overnight uncovered for 8-10 hours
Brush croissants with egg yolk wash, keeping it away from cut edges
Bake at 350°F for 20-25 minutes until browned
