How to Make It
Using a food processor fitted with the slicer blade, thinly slice the frozen butter. Transfer the sliced butter to a plate and freeze. Fit the same bowl of the food processor with the blade attachment. Add the flour and salt; pulse to mix. With the machine on, gradually add just enough water so that the dough forms a ball.
Scrape the dough onto a floured work surface. Roll the dough into a 20-inch-long rectangle, a scant 1/4 inch thick. Arrange the frozen sliced butter in a single layer on the dough. With the short end facing you, working quickly, fold up the dough in 4-inch increments until you reach the end; brush off any excess flour after each fold.
Rotate the dough so that one of the open ends is facing you. Using a rolling pin, gently tap the dough to flatten it slightly, then roll the dough to a 20-inch-long rectangle, a scant 1/4 inch thick. Fold the dough over itself in 4-inch increments until you reach the end; brush off any excess flour after each fold. Repeat the rolling, folding and brushing process 3 more times. Wrap the puff pastry in plastic and freeze until well chilled, about 15 minutes.