In a mixing bowl, combine the flour, salt, sugar, and yeast.
Add cold water and mix until a dough forms.
Knead the dough for about 10 minutes until smooth.
Shape the dough into a ball and let it rest for 1 hour.
Roll out the butter between two sheets of parchment into a rectangle.
Roll the dough into a rectangle and place the butter in the center.
Fold the dough over the butter, sealing the edges.
Roll out the dough again and fold it into thirds.
Repeat the rolling and folding process three times, chilling between folds.
Roll the dough into a large rectangle, cut into triangles, and shape into croissants.
Let the shaped croissants rise for about 2 hours.
Brush with egg wash and bake at 200°C (400°F) for 15-20 minutes.