Place the flour, sugar, yeast, and salt in a large bowl and whisk together until combined.

Slice the butter into 1/8-inch thick slices and toss in the flour mixture to coat.
Add the milk and stir together until a stiff dough forms. 

On a lightly floured surface, roll the dough into a long rectangle shape.  
 Fold it into thirds (like a letter), turn 90 degrees, and repeat 4 to 6 more times, or until the dough has large streaks of butter in it but it is smooth and flat. (If at any point the butter starts to feel soft, chill it in the refrigerator or freezer until stiff.) 


Place on a parchment-lined baking sheet, cover loosely with plastic wrap, and allow to proof until doubled in size (1 to 2 hours). 
 Preheat the oven to 375 degrees F, and gently brush the croissants with egg wash.
Bake for 15 to 20 minutes, or until puffed, golden brown, and flak