Here's the technique and home ec science behind it, as she explained it to me:
A flaky crust requires that small pockets of fat get trapped in the flour/water mixture, melt in the oven, create steam, and puff and leave empty pockets in their wake.
Whatever your recipe, it should include some solid fat -- butter or shortening, or if you are truly old school lard. Said fat should be cold cold cold -- throw it in the freezer before you use it. That will keep it from turning into a paste when you mix it with your flour, water and salt. And your flour should be in the freezer too -- it will help keep the butter cool once it's mixed in.
UPDATE: Having made for the 500th time a not very good crust AGAIN I remembered my mother's other advice: use half butter and half shortening. The shortening -- Crisco -- is absolutely necessary for a tender crust. The butter will make it taste good. Truthfully, my mom's crust is all shortening. So you should probably consider that too. My pie, described at the end \, was nevertheless delicious.
Here's the magic trick:
Divide the butter or shortening in your recipe in half. Put one half back in the freezer. Throw the other half into the food processor or bowl with the flour and salt and cut it or whir it until the butter and flour combine to make a sand-like consistency.
Now, get out the rest of the fat from the freezer, cut it into chunks and put it in the bowl or processor. Give it a QUICK whir - just one or two pulses -- until the new butter is the size of small peas. STOP RIGHT THEN. Add what cold water you need to (plop ice cubes right in the measuring cup) to make it clump. DON'T OVER MIX IT and don't add too much water. Your goal is to keep those peas of butter intact. If you can manage, mix the water in by hand so you keep it under control.
Upend the bowl or the food processor onto a cutting board, gather the dough together into a ball and press down into a disk. Wrap it in plastic wrap. When you look at the top you'll see little balls of butter speckling the dough. VICTORY! Throw it in the fridge for 30 minutes to give the butter a chance to firm up again. Then roll as you would normally and make your pie.
Don't overwork the dough -- too much rolling and rerolling will begin to develop the proteins in the flour (that's what makes bread so spongy and bouncy... kneading develops the protein strands) and give you a tough crust.
Happy Thanksgiving. I'm making this: