In a large bowl, add the water, lemon juice, and sourdough starter. Mix until it is cloudy.
Add the flour and salt. Mix until no dry bits of flour remain. It will be a shaggy dough.
Cover and let the dough rest for 30 minutes.
After the dough has rested, start performing 4-6 sets of stretch and folds.
To do a set of stretch and folds, lift up on one corner of the dough and fold it back into the center of the dough.
Turn the bowl a quarter turn and continue this process all the way around the bowl.
Cover the bowl in between the sets and do these every 15-30 minutes.
On the last set of folds, add the lemon zest and chopped rosemary and continue with the stretch and folds to incorporate the ingredients.
Cover the bowl and let the dough rise for an additional 3-6 hours.
Fermentation time will depend on the strength of your starter. You will know that dough has risen properly when it feels airy and puffy when poked with your finger. The indention should spring back very slowly.
After the dough has proofed, it's time to shape the dough.
Prepare your banneton basket by dusting liberally with flour or you can line it with a tea towel or linen towel and dust with flour.
Turn the dough onto a lightly floured surface and basically perform another set of stretch and folds to shape the dough into either a round loaf shape or oval loaf shape.
Turn the dough over and drag against the table a few times to build surface tension.
Place the shaped dough into the basket SEAM SIDE UP.
Stitch the seams as much as possible to keep the tension on the top of the dough.
Cover and put in the fridge overnight.
The next day when ready to bake the bread, preheat the oven to 450 degrees F with your baking vessel in the oven while it preheats.
Once preheated, remove the dough from the fridge and turn it onto a piece of parchment paper.
Make a slash in the top of the dough with a sharp knife or razor.
Carefully remove the baking vessel from the oven, remove the lid, and lower the dough on the parchment paper down into the pot.
Return the lid and bake for 20 minutes.
Remove the lid and bake an additional 15 minutes.
Let the loaf cool completely before slicing.