Don’t use a food processor to chop the butter and flour; it warms the butter and makes the pieces too small. Flour amounts are listed by weight (ounces) and volume (cups). Use either measurement.
3/4 lb. (3 sticks) cold, unsalted butter, cut into 1-inch pieces
13-1/2 oz. (3 cups) all-purpose flour, chilled; more for dusting the work surface
1 tsp. salt
2/3 cup chilled water
Put the butter pieces on a large work surface and chop them roughly with a knife. Dump the chilled flour and the salt on top of the butter and use a large knife or a pastry blender to cut the butter and flour together. When well combined (the mixture still will be very dry and rough), add the water, a small amount at a time, and mix with a knife or large spatula or a pastry scraper. You’ll have a very crude, dry-looking mixture, but don’t worry: it all comes together.
Scrape the dough aside to dust your work surface with flour and then begin rolling out the crumbly dough into a 6×18-inch rectangle. Use a flat, plastic scraper (or the spatula’s edge) to fold the two short sides of the rectangle to the center; then fold the bottom end to the top, as if you were closing a wallet. You now have a rectangle that’s roughly 4-1/2×6 inches.
Turn the dough 90° clockwise so that the seam is on the right side. Roll it out again to form a 6×18-inch rectangle. You may need to continue lightly dusting the dough and the work surface with flour to keep the rolling pin from sticking to the dough. Repeat the folding process (you’ll have a small rectangle again), seal the dough in plastic wrap, and refrigerate it for at least 15 minutes.
Remove the dough from the refrigerator and roll it out to a 6×18-inch rectangle. Repeat the fold-and-roll process twice more. The dough should be smooth. Seal the dough in plastic wrap and refrigerate for at least 2 hours.