If you think finding a decent gluten free flour mix is a conspiracy, you're right. I've tried every mix, every hyped product, every single thing on the market. Or at least as of October 2009. Since then, I've found that the "magic mix" isn't so magical. The only thing closest to what I wanted was Pamela's Amazing Bread Mix, but it was far less than perfect or amazing. It was sweet. Which as I found out during an experiment with fried chicken, is not as great as someone might think. And it was expensive, even with Amazon's 15% subscribe and save discount. I wasn't happy. And I wanted enough money to actually eat during the month. So now, I mix my own flour.
I use proportions for my mixes. This "all purpose" mix comes with one caveat--it ain't all purpose! I'm telling you all up front that it works great with cookies and breads, but is not so great with more delicate things like cakes, muffins, and tea breads. The high starch ratio gets in the way. That lovely snap in your cookie? That's starch baby. The structure in the bread you make? Starch at work! But when you want a tender crumb, high starch is not the way to go. For all my recipes, I denote what I did. If it's a cookie, I almost always use this mix, but if it's something like cake, I will specify exactly what I use. After all, I really hate all size fits all, don't you? Gluten free baking is a science, a chemistry experiment, and it screws with us enough to just make it interesting. So, to reiterate--don't use this for cake or muffins or cupcakes please!
My go-to basic gluten free mix is:
1 part sorghum flour
1 part tapioca starch
1/3 part millet flour
1 tsp xanthan gum per part
I use Twin Valley Mills for my sorghum flour. I buy a case of four (4) 2.5 lb containers for $17.50 plus shipping, usually around $10 for me.That's around $2.75 per lb. That's cheap my friends. I buy my tapioca starch locally in town, stored in a gluten free area. I buy my millet flour through Amazon, which is quite a bargain. Xanthan gum, again, I buy locally in bulk, for cheap, in a dedicated area.
If you're going to make your own mix beyond this, keep in mind three things: weight, taste, and balance. Some flours weigh more than others. For instance, rice flour is quite heavy. To balance it, you have to play with the starch and the supporting millet. The proportions wouldn't be the same. Some flours have a stronger taste than others. Quinoa flour, no matter how much I love it, has a strong taste, so it needs to be used in smaller quantities. It's also quite light, so again, the proportions need to be tweaked. Finally, balance needs to be achieved for whatever the purpose is for your flour. My balance is achieved by being very bland in taste. Being bland means that it can be used in more places and with all kinds of flavors. It won't overpower most anything. Finally you have to keep in mind the cost...the flours I used are fairly inexpensive. You might love hazelnut flour, but it might break your budget too!
If you need advice beyond this, Karina is the true voice of reason when it comes to gluten free baking and substituting and why reinvent the wheel? Check out her Cooking & Baking Tips!