First you need a sourdough starter. I made mine for a different sourdough that needed too much attention. Good tutorial here (although my original starter only had one grain of yeast, not one packet!).
I keep my starter in a glass jar covered with fabric in the fridge. The night before I want to bake bread, I get out my big bread bowl.
Into the bowl:
4.5 c. whole wheat flour
1/2 to 1 c. starter
Add 3 and 3/4 c. lukewarm water while stirring, until a thick pasty batter is formed. Beat well. Cover (I use a platter).
First replenish the starter by removing 1/2 to 1 c. from the sponge (the overnight mixture) and adding it to the starter.
Then dump into the remaining sponge:
1/2 c. oil
1 Tbs. salt
5-6 c. flour (I use 2 cups unbleached, the rest whole wheat)
When dough comes easily away from the bowl but is still a bit sticky, knead for 5 minutes. Dough will be a little softer and stickier than commercial yeast dough. Cut dough into 3 equal lumps and shape into loaves. Place loaves in greased bread pans. Slit tops with a sharp knife. Cover with a damp dishtowel. Allow almost all day for rising (when I see the dough rounding up the towel) and don't expect it to double in volume. Heat oven to 425. Brush or spray loaves with water. Bake at 425 for 20 minutes. Spray/brush with water again and turn oven down to 375. Bake for 15 more minutes. Turn out on rack and cool before slicing.
The night before:
The next day after kneading:
Tucking the loaves of dough in for a long rise:
Risen! Ready for the oven:
Done. The house smells like heaven. Glow of satisfaction.
I love that this bread is made from flour, salt, oil, and water. It is so unfussy, too - give or take a few hours rising and it's fine. Recipes that demand long stretches of attention or care at critical points do not work well with my life at home with children. My yeast bread suffered from this neglect, but hallelujah! sourdough does not. Occasionally I still make yeast breads for special occasions, but I still gravitate towards ones that have a long rise: in the refrigerator or in the manner of No-Knead.
As for the starter, I bake bread about every other week and it thrives just fine. Sometimes I forget to replenish the starter before I add the oil and salt to the sponge, so I just use plain flour and water. Possibly I am grossly mistreating my starter or overlooking a key step in my baking - I still have a lot to learn about sourdough, but for 8 months now, it's been working fine.