Cook's Illustrated Gluten-Free Flour Blend

I bought the Cook's Illustrated gluten-free cookbook recently.  In the ads, they hyped their flour blend recipe as being the best thing since sliced bread.  I was a little dubious but their track record is pretty good.  Anyway, I made their flour blend, which isn't too obscure or pricy, at least by gluten-free standards.  It has brown and white rice flour, tapioca starch,  potato starch and a little bit of non-fat milk powder.  From there, I tested the chocolate chip cookie recipe and the waffle recipe.  These are things that I haven't been able to replicate very well.  Much to my surprise, they both came out really well.  As in, 'I can't believe it's gluten-free!' well, even though I took some liberties with their flour recipe (see below)  Even more surprising, the recipes were actually less full of special tricks than the average Cook's Illustrated recipe.  So I am going to share the flour blend recipe, but I do recommend buying the book if you're going to be doing a lot of gluten-free baking.  It is awesome and I am looking forward to trying more recipes.

For the flour blend, they recommend using Bob's Red Mill rice flours.

Gluten-Free Flour Blend
24 oz white rice flour (4 3/4 cups, or a standard size pack from Bob's Red Mill)
7 1/2 oz brown rice flour (1 2/3 cups)
7 oz (1 1/3 cups) potato starch
3 oz tapioca starch (3/4 cups)
3/4 oz (3 tbsp) non-fat dried milk powder

Whisk all ingredients together well.  Store in a ziplock bag.

I have a confession to make - I didn't totally follow their recipe since I was running low on a few things.  So I used more like a half and half mix of brown and white rice flour, and a little bit less potato starch and a little bit more tapioca starch.  Even so, the recipes came out better than any other gluten-free recipes I've tried, even ones using pricy flour blends.  So I'm going to guess that the relative proportion of rice flours to starch is important, but the relative amounts of brown vs white rice flour, or tapioca vs potato starch, are less important.  The milk powder is important since it helps with browning and contributes protein.