Toast flax seeds in a skillet until they start crackling and smell toasty. In a medium bowl, combine flax seeds with 320g (1.5 cup) water. Set aside.

In a large bowl, whisk 320g (1.5 cups) water with the starter until milky and bubbly. Add 500g (4 cups) of sifted spelt flour (I use a fine sieve; mix with a spoon until no dry bits remain (the dough will be sticky). Cover and leave for 30 minutes.

At the end of 30 minutes, add flaxseed mixture and salt. Mix with large spoon or stiff spatula to incorporate the seeds. Add the rest of the flour; mix to combine with a spoon first, then with your hand. Keep dipping your hand in water up to your wrist and knead using stretch and fold movements until flour is incorporated. The dough will be sticky. Cover tightly and leave at room temperature for 30 minutes.

Now you have a choice - to cover the dough and leave it at room temperature for 8-10 hours, until it significantly increases in size - OR - to perform several rounds of stretch and fold, described right below (S&F helps the dough develop better leading to a fluffier bread with more open crumb).

Wet your hand to your wrist (to keep knuckles from getting sticky), and do a series of 'stretch and fold' - grab the underside of the dough, stretch upwards, then fold on top of itself. Rotate the bowl quarter way, grab another side of the dough, stretch and fold again. Do that four times. And repeat the same steps 5-6 times every 30 minutes. At the end of that time, the dough will feel full, soft and billowy.

After all the rounds of stretch and fold, leave the dough to ferment for 4-6 hours, until it doubles in size.

Very gently, trying not to deflate the dough, use a spatula to separate half the dough into another bowl. Allow the dough to rest again for 30 minutes. Put a Dutch oven with lid into your oven, turn it on to 475ºF (250ºC), and set timer for 20 minutes. Put Dutch oven on the counter, remove the lid, and gently pour (yes - pour!) the dough into the hot Dutch oven, using a soft spatula to scrape all the dough from the bowl.

Put the lid back on, transfer to the oven and bake for 20 minutes. At the end of 20 minutes, remove the lid, and continue baking for 20-25 more minutes. Don't go beyond 30 minutes uncovered trying to achieve deep brown color, there is something about flax seeds that prevents crust from getting really brown.