Grating frozen butter is a crutch and you know it. When you cut butter by hand you feel the flour change under your fingers, you learn when to stop, and that feel is what lets you fix a dough that's too dry or too warm on a humid day. A grater gives you the same size shreds every time, which sounds great until you want a mix of big and small butter bits for a crust that's flaky in some spots and tender in others. Ruth ran a bakery with machines doing half the work, so of course she pushed the fast way. Ask yourself what happens when your grater breaks or the butter thaws on the counter, then you're back to square one with no skill to fall back on. Keep the slow way for a month and watch how much better you get at reading the dough, that lesson is worth more than 90 seconds saved.