About 1 hour before you think your starter will be ready to use combine the warm water and both flours in a large bowl. Cover with a damp cloth and allow to sit for 1 hour.
After 1 hour add the mashed garlic, minced rosemary, 90-100 grams of active starter and 10 grams of salt to the dough. Begin kneading the dough using the slap and fold technique. Do this for about 5 minutes or until the dough begins to come together. Cover the dough with a damp cloth and let it rest in a warm place for 30 minutes.
After 30 minutes, stretch and fold the dough. Cover and let it rest for 15 minutes. Stretch and fold again, let it rest for 15 more minutes, repeat this process one more time. A total of 3 15-minute intervals.
Now stretch and fold the dough, cover and rest for 30 minutes. Repeat this process two more times for a total of 3 30-minute intervals.
Cover the dough and let it bulk ferment for several hours. The dough will be ready to shape after it has doubled in size. This can take anywhere from 5-8 hours, depending on the temperature. Even longer if bulk fermenting in a cold spot.
Shape and place in your dough in a floured banneton or bowl. Or you can line a bowl with parchment paper for easier pick up if you want to transfer the dough straight from the bowl to the dutch oven. When doing this method place the dough seam side down on the parchment. Cover with a plastic bag and refrigerate overnight. Aim for 12-24 hours.
1 hour before baking preheat your cast iron dutch oven in a 500°F oven. When ready lightly flour the cast iron, invert the dough onto the hot cast iron and score. Cover the dough and place in the oven for 20 minutes. After 20 minutes reduce the heat to 450° F and remove the top cast iron pan. Bake for another 20 minutes. Cool completely before slicing. Enjoy!