I've been using an adapted recipe for flatbread from the book Going Gluten Free by Mary Brown. I have since simplified the way I make the recipe and made a few adaptations (such as changing the egg ratios to reduce egg white since my kids are sensitive to too much egg white).
3 tsp sugar dissolved in:
1 1/2 c warm water
2 tsp yeast
3/8 c oil
1 1/2 tsp vinegar
2 1/4 c. flour from GF grain (not a baking blend--I usually use a ratio of 1/3 millet, 2/3 brown rice, and sometimes I throw a little oat or jasmine rice flour in)
1 c starch (I usually use half tapioca, half potato)
3 tbsp sugar
2 tsp xanthan gum
1 1/2 tsp salt
1 tsp gelatin (1/2 pckg)
Preheat oven to 375 degrees. Dissolve 3 tsp sugar in 1 1/2 c warm water. Dissolve yeast and add vinegar and oil. Combine flour, starch, sugar, xanthan gum, salt, and gelatin in a bowl and mix. Pour into mixersuch as a Kitchen Aid or Bosch and add eggs. Mix for about 5-10 minutes. While batter is mixing grease a jelly roll pan. Spread batter onto pan.
At this point you can either let it rise or bake it. I prefer to just bake it. If you let it rise you will have fluffier bread but it will also feel chalkier and fall apart more easily. I get better sandwiches when I do not let it rise.
Bake at 375 degrees for about 20 minutes. The pull it out and let it cool. Freeze or eat immediately. I cut mine into squares and when it cools I remove the slices with a spatula and put them in a gallon size ziplock freezer bag. It stays good in the freezer for a couple of weeks. I often make a double batch and that works okay, although your second batch will have longer to rise than the first.