Step 1Cover and freeze the butter and flours for 30 minutes to chill thoroughly.
Step 2In the bowl of a food processor, combine the all-purpose and cake flours, along with the salt. Pulse to combine.
Step 3Add half of the frozen butter pieces and pulse until the butter is reduced to the size of peas. Add the remaining half of the pieces, and continue to pulse until the size of peas.
Step 4Slowly add the water and lemon juice, and continue to pulse just until the dough begins to clump together.
Step 5Remove the dough to a floured board (using all-purpose flour), and form into a rectangle about 12 by 8 inches.
Step 6Fold the dough in half (the dough will be very crumbly at this point), then roll out again until the dough measures a 12-by-8-inch rectangle.
Step 7Fold the dough in half again, then cover and place in the freezer for 20 minutes.
Step 8Remove the dough and roll out into a rectangle. This time, fold the dough into thirds, as with a letter. Roll the dough out once more and fold again into thirds. Roll out and fold once more.
Step 9Cover and chill until ready to use.