Stir down your sourdough starter and measure 3 cups into a large mixing bowl.
Add the 1 1/2 cups water and mix that up until it's smooth. This is where I add the yeast if I'm using it. You can put it in the water to dissolve, or sprinkle it over and mix it in.
Mix the yeast in well.
Then add 3 cups of flour and mix the flour in until blended.
. Salt can kill yeast, so I like to protect the yeast with some flour first.
Sprinkle the salt on top of the mixture and mix that in well.
Continue to add flour a little at a time until the dough forms a ball.
Now, turn your dough out onto a floured surface. Knead the dough, adding flour as necessary, until the dough is no longer sticky. About 15 minutes.
You can also do this step in the stand mixer with the dough hook. For about 8 minutes.
Oil a bowl with butter or any other neutral tasting oil and place the dough in it. Turn the dough over so that the top is now oiled.
Without extra yeast it will take anywhere from 4 to 6 hours. With yeast it will be anywhere from 1 1/2 to 2 hours.
Punch the dough down and divide into 3 pieces. Form into loaves.The loaves will be about 1 1/2 pounds, give or take.
Oil the baking pans, (again, I use butter) and place the loaves in the pans.
Cover again, and let rise till doubled. This rising should take only about half the time it took for the first rising.
Preheat the oven to 350°F degrees.
When the loaves have doubled, brush the tops with melted butter. This will give the loaves a golden color and a crispy top crust.
Slash the tops with a lame or a sharp serrated knife.
Put the loaves in the oven and bake for 30 - 45 minutes.
The tops will be golden and the bottoms will sound hollow when you thump them with your finger.
Turn out of the pans on to a cooling rack. If the bottom crusts don't have as much color as you would like, put them back in the oven without the pans for a few minutes.