Using a rolling pin and parchment paper, pound the butter into a thin rectangle 30 cm x 15 cm. )I find using a bench scraper works great to even out the edges within the parchment paper without getting it dirty.) Refrigerate.
Proof yeast in warm water. In a separate large bowl, add flour, salt, sugar and melted butter. Stir in proofed yeast and water. Knead gently to create dough. Cover with plastic wrap and rise 30 minutes on the counter and then refrigerate for a minimun of 2 hours (but up to 6 hours.)
Once dough and butter block are cold, roll the dough out to a rectangle approximately 50 cm x 17 cm. (A little larger is fine and normal.) Place butter block onto one side of the dough. Fold extra dough overtop of the butter block to cover half of the butter.
Fold other side with butter and dough overtop the first fold. You should have five total layers: dough, butter, dough, butter, dough.
Roll out to be a large rectangle and then create a double fold or book fold: fold the two edges in towards the center and then fold those edges in again. Wrap in plastic wrap and refrigerate 1 hour.
To create more layers, roll rested dough out to a rectangle and fold another double fold or book fold. Wrap in plastic wrap and refrigerate 1 hour.
Roll dough out to be a 4 mm thick rectangle, approximately 50 cm x 25 cm. Trim any extra dough to make the rectangle as accurate as possible. Cut triangles that are 10 cm wide and 25 cm long.
You should get 10 full size with a few smaller ones made with scraps of dough. Roll triangles into croissants and place onto baking sheets.
Brush croissants with beaten egg and rise 2 to 3 hours or until croissants look and feel puffy and have doubled in size.
Brush Croissants with more egg wash and bake at 400 degrees for 15 to 20 minutes or until golden brown in color, including the creases. Remove from oven and transfer to cooling rack. Enjoy warm or at room temperature.