If you have an active starter, you can feed it the night before starting the dough. Otherwise, feed your starter twice a day until it's doubling within six hours. Then feed it again the night before you want to start the dough.
The morning after feeding your starter (or six hours after feeding it). Weigh and combine all ingredients in a large bowl or the bowl of your stand mixer. Knead for 8 minutes with your stand mixer on medium. If you are doing this all by hand, you will need to knead for at least 15 minutes to get a smooth, but slightly tacky dough.
The dough should be smooth, but it may feel a little grainy from the semolina flour depending on how finely milled the brand you bought is. Once smooth and kneaded, shape the dough into a ball and place it in a lightly greased bowl, cover it with a lid, large plate, or plastic wrap and keep it in a warm spot in your kitchen.
Allow the dough to rest for 1 hour.
After the dough has rested for 1 hour, you should perform a stretch and fold of the dough. If you're not familiar with stretch and fold, I suggest you watch this YouTube video: How and when to stretch and fold. Once you have stretched and folded your dough several times, tuck it back into your bowl to continue resting.
After a second hour, perform another stretch and fold, and allow the dough to rest for another 2 hours untouched.
At this point, your dough should have spent 4 hours resting and rising. Now it is time to shape. Perform another stretch and fold, but this time you will want to end with your dough in the shape of the container that you are planning to use for a final rise. If you have a banneton (oval bowl for dough shaping), you will want to shape your dough into an oval. If you are planning to use a medium-sized bowl for the final rise, you will want to shape your dough into a taut ball.
Flour the inside of the banneton or bowl very lightly and place the dough into it upside down with the smooth side touching the floured container. Lightly flour the visible dough and cover the banneton or bowl with plastic wrap.
Allow dough to rise for another 2 to 3 hours or until the dough has about doubled in size.
After the final 2 to 3 hours of proofing, store the dough in its bowl or banneton covered with plastic wrap in the fridge overnight or at least 3 hours.
Once you are ready to bake, preheat the oven to 450 F (230 C).
Grab a large Dutch oven but do not preheat it.
Carefully slide out your shaped and risen dough onto a piece of parchment. Score the dough with a very sharp knife and then holding the parchment corners, gently place the dough and parchment into the Dutch oven. Cover the Dutch oven with the lid.
When the oven is preheated, place the Dutch oven in the oven and bake with the lid on for 25 minutes. Remove the lid and bake for 15 more minutes.
Bake directly on the oven rack for up to 10 more minutes if you want a bit more color.
Notes:
Required tools for this dough: A Dutch oven large enough to hold a loaf of bread while it bakes.
Here's King Arthur Baking's recipe for making a sourdough starter. You can also buy a live starter from King Arthur and I have tested this method and it works great. If you're buying it, I would suggest paying extra for shipping to get going with the starter sooner.