Mix flour, sugar, salt, yeast, and 350-400ml cold water into a soft dough.
Knead the dough on a floured surface for 8-10 minutes until smooth and elastic.
Roll chilled butter between greaseproof paper into a 30x20cm rectangle about 1cm thick and chill.
Roll the dough into a 60x30cm rectangle on a floured surface.
Remove paper from butter and place centrally on the pastry rectangle.
Fold both edges of the pastry over the butter to cover it completely.
Fold the rectangle in half lengthways, turn a quarter, and roll to 60x30cm again.
Repeat the folding and turning process three more times then chill overnight.
Roll pastry to 0.5cm thickness and cut into 10cm wide triangles.
Stretch the base points of each triangle outwards slightly.
Curl the pastry into a traditional crescent shape toward the narrow point.
Repeat for all triangles until approximately 20 croissants are formed.
Place on lined trays, brush with beaten egg, and prove for 30-45 minutes.
Bake at 190°C for 20-25 minutes until golden-brown and serve warm.