There are two secrets to making light, flaky pastry dough in a food processor: Use cold ingredients and process the dough as little as possible.
Put 5 cups flour and ¼ tsp. salt in the bowl of a large food processor fitted with a metal blade. Pulse a few times to combine, then add ¾ lb. very cold unsalted butter cut into small pieces, and pulse until mixture resembles coarse meal, 10-15 pulses. Add 3 egg yolks, then slowly pour in 4 tbsp. ice water while processing for 15-20 seconds. Pulse several times until dough just comes together. Don't let it form a ball; if dough holds together when you pinch a piece, it's ready. Transfer dough to a resealable plastic bag and form into a flat round. Chill 1 hour before rolling out.