*I make my GF flour mix ahead of time and store it in Tupperware containers and then use it measure for measure for the flour called for in any recipe. I use three parts Asian white rice flour and two parts Argo cornstarch. With the packaging that’s available for each, I usually use three 1-lb packages of Asian white rice flour and two 1-lb packages of Argo cornstarch. I am sure superfine brown rice flour could be used instead of the white rice flour. If you require lower glycemic index grains for your flour mix, you may have already come up with an alternative GF flour mix, but this one works best for me in all my recipes.
Some people recommend piercing popovers when they reduce the oven temperature at the half-way point (or at the very end and leaving in another minute or two), to make them drier. That’s up to you, but dry is typically NOT something we are looking for in gluten-free recipes. I love that these are super moist; that factor is especially great for reheating. Of course, if you are a reader who eats gluten with no issues, all-purpose flour can be used and the xanthan gum omitted.