In the bowl of a food processor or using the paddle of an electric mixer, mix 1/2 cup flour with the butter until combined and very smooth. Transfer to plastic wrap and shape into a flat square 1-inch-thick, wrap well, and chill for at least 30 minutes.
Combine the salt with the remaining flour in a large bowl, and add the cream. Mix well by hand or with the paddle attachment of an electric mixer; the dough will not be completely smooth but it should not be sticky. Shape it into a flat square 1 1/2 inches thick, wrap in plastic, and chill, at least 30 minutes.
Remove the flour dough from the refrigerator. On a lightly floured board, roll the dough into a rectangle twice as long as the butter dough. Place the butter dough in the center, fold up the ends to completely encase the butter dough, and seal the edges by pinching them together. Wrap well in plastic, and chill for at least 30 minutes, so that the dough achieves the same temperature throughout.
Remove the dough from the refrigerator. On a lightly floured board, roll it out into a large rectangle approximately 1/2 inch thick. Fold the dough into thirds, aligning the edges carefully, and brushing off any excess flour. The object is to ensure that the butter is distributed evenly throughout so that the pastry will puff evenly when baked. Wrap the dough, and chill it for at least 30 minutes. This completes one turn.
Repeat this process five more times. Be sure to use as little flour as possible when rolling out the dough, and always brush of any excess. Remember to let the dough rest for at least 30 minutes in the refrigerator between turns, or 15 minutes in the freezer. This chilling makes the rolling out process much easier, and it keeps the layers of butter of equal thickness.
By the sixth and final turn, the dough should be very smooth, with no lumps of butter visible. Wrap the pastry in plastic wrap, and refrigerate until ready to use (up to 2 days), or freeze for future use.