If you have oat flour, it's one cup but if you are grinding the
oats in your
food processor, you need to start with 1 1/3 cup
oats and don't
over process (that's partly why mine look so grainy since I started with
oats and not oat flour).
To have these cookies turn out flat, you don't want to
over ground the
oats, just a couple quick pulses
in the
food processor to break them up a bit.