Measure the sourdough into a cup, and add enough room temperature water to equal 1 1/2 cups. Stir the starter to dissolve it in the water.
Pour the starter-water mixture onto the flour. Stir together until all of the flour is incorporated. (I just mix with my hands). It's important to make sure all of the flour is incorporated.
Cover with plastic wrap and a towel, and leave overnight in a room at about 70 deg. F. for 12 to 18 hours.
At this point, the dough should be quite puffy. Lightly oil your hands. Without removing the dough from the bowl, fold the edges of the dough into the center. Once you've gone all around, pick up the dough, pull it to a rectangular shape and roughly fold one end over the other (like folding paper for an envelope). Do it again, pulling from the opposite edge. Now plop it back down into the bowl. Cover and let rise and additional two hours.
About 30 minutes before the two hours is up, place your pot with its lid (3 to 4 qt size) in the oven and heat your oven as hot as it can get. (Grease your pan if you feel it might stick).
When your dough is doubled, pull the pot from the oven and very carefully remove the lid. Tip the dough right into the pot (a silicone spatula helps tremendously), cover, and return to the oven. (Also, see Katzen's review for a great suggestion on using parchment paper to simplify transfer).
Reduce temperature to 450 deg. F. and bake for 30 minute Remove the lid and bake an additional 15-30 minutes.
Remove loaf from pot and allow to cool before slicing.
Note1: A plastic bowl or basin really works well. Get one that has a smallish flat area at the bottom - this will help shape your loaf.
Note2: Thanks, Zurie, for reminding me of the mix in the bowl technique - my late aunt first taught this to me, but I'd forgotten about it. It really works and you end up with much less cleanup.
Note3: Starters vary tremendously in how liquid they are. You may need to add a little water to get the right consistency. Remember, this dough is not going to look like a traditional dough in the first phase. It should be soft but not gloppy or liquid.
Note4: Substitute 6 ozs. of wheat flour for 6 ozs. of white flour for a heartier loaf.
Note5: It's sometimes difficult to visualize what a doubled loaf looks like. Remember that a 10" diameter ball has double the volume of an 8" diameter ball. Don't let your bread overrise.