I began this recipe collection as "Operation Quaker," and it's no accident. The only oatmeal I use in my oatmeal cookies is Quaker Old Fashioned Oats. In fact, Quaker was the oatmeal my grandmother used to make her oatmeal cookies. And you know there’s no going against grandma.
I use "old fashioned" oats in my oatmeal cookies, not quick oats or instant oatmeal, because I’ve found that the old fashioned oats produce a cookie with the best texture. Quick oats and instant oatmeal are par cooked and have a mealy texture that doesn’t quite carry over to cookies. Just open an envelope of instant oatmeal and you’ll see what I mean: Are there oats in there, or is it flour?
If you’re making a recipe that calls for finely ground oatmeal, though, I guess quick oats or instant would work in a pinch. But be warned: The cookies' texture and flavor will likely be a little pasty.