Ingredients

150g bubbly, active starter
250g warm water, preferably filtered
25g olive oil (optional see below)
500g bread flour (not all purpose flour)
10g fine sea salt
Flour for dusting
NB: The olive oil makes bread with more, smaller bubbles, if you like it with big and little bubbles don't use it.

Method

To make the dough: Whisk the starter, water, salt and olive oil in a large bowl.
Add the flour and squish everything together with your hands until all of the flour is absorbed. Rest (autolyse) for 30 minutes.
After the dough has rested, work the dough in the bowl into a rough ball, about 15 seconds.
Bulk fermentation:
Cover the bowl a clean, damp kitchen towel. Leave it in a warm, sunny spot to rise. Your dough is ready when it no longer looks dense, and has increased in volume about 1½- 2x its original size. You should see bubbles on the surface and around the sides (if you have a see through bowel) This can take anywhere from 3-12 hours depending on the temperature of your ingredients, the potency of your starter and surrounding environment.
Stretch & fold
During bulk fermentation, you have the option to perform a series of ‘stretch & folds’ to strengthen the dough. Simply gather a portion of the dough, stretch it upwards and then fold it over itself. Rotate the bowl ¼ turn and repeat this process until you have come full circle. Do this once or twice spaced an hour apart. Although this step is not mandatory, it will increase the total volume of your bread.
Cutting & shaping: To cut and shape the dough, divide your work surface in half; lightly flour one side (for cutting) and leave the other half clean (for shaping).
Remove the dough from the bowl, place on the floured section so that it does not stick. You do not need to ‘punch down’ the dough; it will gently deflate as you fold and shape it.
Cut the dough in half to make 2 loaves, or leave it whole for a single loaf.
To shape, use a bench scraper to move your dough to the non-floured section (if there is any flour present, it will be difficult to shape- brush away any excess). Starting at the top, fold the dough over toward the center. Give it a slight turn, and then fold over the next section of dough. Repeat until you have come full circle. Then flip the dough over and place it seam side down. Using your hands, gently cup the sides of the dough and rotate it, using quarter turns in a circular motion. You can also pull it towards you to even out the shape. Repeat this process until you are happy with its appearance. You are aiming to create surface tension, the skin should look tight when you are finished.
Second rise:
Use a Dutch oven or casserole dish with a lid. Coat the bottom with flour or use baking paper to prevent sticking. Place the dough inside for a second shorter rise, about 1-2 hours. It is ready when the dough is slightly puffy.
Slashing the dough: Just before your bread goes into the oven, make a shallow slash about 2 inches long in the center of the dough. You need a very sharp knife or a pair of scissors.
Preparing the oven: When ready to bake, preheat your oven to 220c, 450 F
Place your bread into the oven (lid on) and reduce the temperature to 200c 400f, bake for 30 minutes. Remove the lid, and continue to bake (uncovered) for an additional 30 minutes or until deep, golden brown. Keep in mind that all ovens are different; you might have to make adjustments to these temperatures or times.
You can take the internal temperature of your bread to double check that it is done. For sourdough, it should read about 205 F, 100c
Cooling: Remove the bread from the oven, and cool on a wire rack for at least an hour before slicing. Don’t cut too soon or else the inside will have a gummy texture!
Notes
You can improve the flavour of your loaf by putting the mix in the fridge during the bulk fermentation or second rise for 12 hrs plus.
When you make the slashes you cut through this tension allowing the loaf to rise more easily.
You can adjust the crunchiness of the crust by altering how long you leave the lid on. For instance, if you find the 30/30 minutes ratio makes the crust too crunchy try 40/20.
Try mixing a percentage of rye or wholemeal flour with the white flour. Keep the overall weight the same.