In a heavy weighted mixing bowl add the lukewarm filtered water and active sourdough starter. Using the danish whisk, whisk until the starter is dissolved in the water.
Add the flour. Using the Danish whisk mix the flour in the best you can without kneading. It should be a dryish-looking shaggy dough. Cover with a damp kitchen towel and set into your kitchen sink filled about half full with warm water for 30 minutes.
Next add the salt and additional 30 grams of water. Using your hands incorporate the salt and water into the dough until it is thoroughly incorporated. Cover with a damp kitchen towel and set into your kitchen sink filled about half full with warm water for 30 minutes.
Begin a series of stretches and folds every 30 minutes over 2 hours. Do this by pulling the dough up as far as it will go and then folding the dough back over. Turn the bowl a quarter turn and repeat this process 4 times. Between each stretch and fold cover with a damp kitchen towel and set into your kitchen sink filled about half full with warm water for 30 minutes.
After the last stretch and fold set the bowl back in your sink of warm water for 3 hours to allow for bulk fermentation. (refresh with fresh warm water if needed) The dough should double in size. If it didn't double in size allow to set for an additional 30 minutes or until it doubles in size.
Turn the dough out onto a very lightly floured surface. Laminate the dough by gently stretching the on each side until you have a sheet of dough. Fold the dough over itself in thirds and begin rolling the dough up into a ball.
Preheat the oven to 480°F. Build tension in the dough by pushing the dough ball up and pulling it back down. When shaping your loaf, be gentle but firm in creating surface tension on the outside of the dough. This will help prevent it from spreading out too much during baking and promote oven spring.
Place the dough into a banetan basket and cover. Place into the freezer for 15 - 20 minutes. This will help with the scoring process.
Turn the dough out onto a sheet of parchment paper. Using a bread lame score the dough. Pick the dough up using the parchment paper and place into the cast iron Dutch oven with lid. Put in oven and allow to bake at 480°F for 45 minutes. After turn the oven down to 350°F. Remove the dutch oven lid and allow to bake for 20 minutes.
Notes
How to StoreJust like any sourdough bread store it in an airtight container or bag. Keep it in a cool dark place and it should last 4 - 7 days if stored properly.