Make the butter dough: In the bowl of a food processor or using the flat paddle of an electric mixer, mix 1/2 cup flour with the butter until very smooth. Shape the mixture into a 1-inch-thick flat square, wrap well in plastic, and chill for at least 30 minutes.
Make the flour dough: In a large mixing bowl, combine salt with the remaining flour, and add cream. Mix the dough well by hand or with an electric mixer; the dough will not be completely smooth, but it should not be sticky. Shape it into a 1 1/2-inch-thick flat square, wrap in plastic, and chill for 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 square. Place the butter dough in the center, fold up the ends of the flour dough 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, and 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; classic puff pastry gets six turns, creating hundreds of layers of butter between layers of the flour dough (729 to be exact). Use as little flour as possible when rolling out the dough, and always brush off 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 rolling out the dough much easier and keeps the layers of butter equally thick.
By the sixth and final turn, the dough should be very smooth, with no lumps of butter visible. Wrap the pastry in plastic wrap; refrigerate until ready to use (for up to 2 days), or freeze for future use.