WOW! WOW! WOW! Did I say Wow! This is exactly what I have been looking for, a low carb bread as I am a diabetic. I did not know that arrowroot is a carb but I calculated that 1/2c. equals 72 g. of carbohydrates roughly. So not too bad. I have enjoyed every recipe I have tried so far. I can’t tell you how happy I am that I accidentally discovered your website. Keep up the good work!! I just can’t stop making everything I see. ?
Once your yeast is proofed, add in the egg, egg whites, lightly cooled melted butter (you don't want to scramble the eggs or kill the yeast!) and vinegar. Mix with an electric mixer for a couple minutes until light and frothy. Add the flour mixture in two batches, alternating with the sour cream, and mixing until thoroughly incorporated. You want to mix thoroughly and quickly to activate the xanthan gum, though the dough will become thick as the flours absorb the moisture. 
This was awesome. This is my second attempt at a no wheat bread. I did one before with coconut flour and it tasted like a salty cake. This is perfect. And I had to make few substitutions. Can’t wait to try the original recipe as I know it will taste even better. I had to substitute the flax meal and seeds with ground sesame and sesame seeds (no background on this, I made it up because I didn’t have flax seeds) and used olive oil instead of butter because I was too anxious to get it done and didn’t want to wait the melted butter to cool off. Even with this changes it browned perfectly, and it’s so fluffy!!! I’ll try toasting it to get a harder texture to be able to use it with toppings. Thank you very much for this recipe. 5 stars!!!