Measure flour and salt in a large mixing bowl.
Cut in cold butter with a pastry blender until it resembles coarse crumbs.
Pour water into a well in the center of the flour.
Mix and knead for a few minutes until the dough becomes smooth.
Chill dough for 30 min. Wrap in cling wrap.
Mix room temperature butter and flour together. Shape into a 9" square by beating it with a rolling pin in between 2 cling wrap pieces on a cutting board.
Roll the dough out to a 12" square. Place butter in a diamond shape on the dough.
Close the dough around the butter like an envelope and seal the edges so the butter is fully enclosed.
Use flour as needed to roll the dough into a rectangle shape until its ~ 1/4" thick. Fold the dough like a letter. Fold one side over the center. Then fold other other side over the center creating 3 layers of even size.
Roll out the dough into a rectangle again and repeat the letter folding process. Chill for 30 min.
Repeat this process until you have completed 6 folds, chilling for 30 min in between every 2 folds.
Your puff pastry is ready to be used.