Combine warm water (like bath water, or 110 degrees F / 43 C), yeast, maple syrup or sugar, salt, flax seed and flours in a large mixing bowl and stir. The result will be a sticky, rough dough. If using a stand mixer, beat at medium speed for about a minute. Otherwise just use a spoon to stir until well combined and when it can no longer do the job, knead and turn it in the bowl with your hands. Add flour until the dough is no longer sticking to the sides - about 3 3/4 cups total (amount as original recipe is written // adjust if altering batch size).
Preheat oven to 425 degrees F (218 C)* toward the end of the dough resting time and place a metal or cast iron pan (not glass, Pyrex, or ceramic) on the lowest oven rack. Also have 1 cup of hot water ready.
*Based on some users' experience, I lowered the baking temperature to 425* F (from 450) to ensure the middle gets all the way done. I've had success at 450* F, but it seems some people's ovens or loaf pans are not allowing it to cook all the way through. This information was updated 3/15/16.
*Adapted from my 7 Ingredient Muesli Bread.
*Nutrition information is a rough estimate.