Sift the two flours and salt together in a bowl. Quickly cut in the butter by hand. Pour in the cream and stir briefly. The dough should be coarse, and neither wet nor dry.
On a lightly floured surface, pat the dough into a 6-inch square. Roll the dough out into a 12-inch square and fold it over by thirds, using a scraper to help you, forming a 12- by 4-inch rectangle. Remove it from the board and chill for 30 minutes. Roll out and fold again, and chill for 15 minutes, doing this step three more times until the dough is smooth.
Now you’ll need to make a double or “book” turn: Roll the dough out to 14 by 8 inches; fold each 8-inch edge so they meet in the middle, then fold in half. Roll and fold the dough in this way two more times.
Wrap and refrigerate dough for 2 to 3 hours before using.