More trials.....half a loaf is better?

Yet another Gluten-free Bread attempt 

Here's the next episode in my on going gluten-free bread-making saga...lots of hyphens there and more to come! I'm trying to make a (here it comes!) gluten-free, egg-free, dairy-free, nut-free, yeast-free, corn-free  (no xantham gum), soy-free and gelatine-free bread using a gluten-free sour dough starter. Till now, my sour dough starters have been non-starters (sorry,couldn't resist). At last, in my latest attempt, the starter turned out the way I perceived it should. I was so excited! Then I got into the actual mixing and baking. For this loaf, I used a store bought gluten-free bread mix. It was a premix of rice, tapioca and potato flour with xantham gum added. I know I keep going on about xantham gum having corn in it but I figured I'll give the premix a go to see if I could actually make a reasonable tasting gluten-free bread. The bread flour with the sour dough starter mixed up fine. I kept it in my oven with just the light on to let the bread dough rise. Then when I carefully transferred the beautifully risen loaf to a heated pan, poof! My bubble burst......literally. The dough started sinking and I ended up where I started.......with a bookend! Back to the drawing board..........sigh.