In a clean mixing bowl, combine 275 ml/9.3 floz of the water with the levain. Stir until the levain is completely dissolved.
Add the flour and whole grain spelt flour. Mix and squeeze the dough together until all of the water has been absorbed.
Gradually add another 50 ml/1.7 floz of water, taking your time. Over the next 5-10 minutes, work the water into the dough using gentle squeezing motions without tearing the dough.
Once all the water has been absorbed, let the dough rest for 15-20 minutes. This gives fermentation a head start and allows the gluten structure to begin developing.
Next, add the salt along with 20 ml/0.68 floz of the remaining water. Knead for about 5 minutes, until the dough feels smoother and has absorbed the water. Repeat with the final 20 ml/ 0.68 floz of water.
Grease a clean bowl with a little oil. Place the dough in the bowl, cover it, and let it rest at room temperature for 30 minutes.
Keeping the dough in the bowl, wet your hands and gently lift one side of the dough, folding it over itself toward the center. Turn the bowl and repeat from all sides, being careful not to tear the dough. Cover and let it rest for another 30 minutes. This is known as the stretch-and-fold technique, which strengthens the dough without intensive kneading.
Repeat the stretch-and-fold process one more time. Then cover the bowl again and let the dough rise at room temperature for 4 hours.
Dust your work surface with flour and gently turn the dough out onto it. Press it down lightly to flatten it. Meanwhile, preheat your oven to 480°F /250°C (conventional oven) and place your Dutch oven or bread baker inside. It should preheat for at least 30 minutes so it's fully heated before baking.
To shape the loaf, fold two opposite edges of the dough toward the center. Repeat with the other two sides, continuing until you've formed a round ball. Flip the dough over and use your palms to gently rotate and tighten the surface into a smooth, round loaf. Be careful not to tear the dough.
Dust your proofing basket with flour and place the dough inside. Let it proof for at least 30 minutes.
Turn the dough out of the basket, brush off any excess flour if needed, and score the top with one long slash at least ¼ inch (½ cm) deep.
Using oven mitts, carefully remove the hot Dutch oven from the oven. Dust the bottom lightly with flour, place the dough inside, cover immediately with the lid, and return it to the oven as quickly as possible. The hot baking vessel gives the bread an excellent oven spring.
Bake for 25 minutes with the lid on. Then remove the lid and continue baking for another 20 minutes, until the crust is deep golden brown.
Remove the bread from the Dutch oven and let it cool completely before slicing. This will take at least 1 hour.