Put the starter in the large bowl with 1 cup of water and the blackstrap molasses. Mix well.
Add your salt and flours and mix it up.
Add the remaining 2-3 cups of water. The amount of water you add will be dependent on the type of flour you are using. Your dough must be moist and might even be a little sticky (rye flour is more sticky than wheat flour). You may use your hands or a scraper or even a spoon to mix it all up. There is no need to knead the dough very well or long here, just mix it up to incorporate all the ingredients.
Cover the dough with a lid and leave it overnight to rest and rise.
In the morning, gently pull up the sides of the dough towards the middle and then divide and shape the dough into two equal parts if you are making two loaves (or shape it into one big round bread). Work with the dough lightly. Wet your hands, or the utensil you are using, just slightly with a little water so as to work a little easier with the dough. Alternatively use a little bit of flour to dust your hands or the utensil, but don’t be tempted to keep adding flour.
At this point you can leave the bread to rise overnight and bake it in the morning. Sourdough bread has a longer rising time than normal bread - it will take at least 4-5 hours.
The next morning, have your oven nice and hot at 200°C and place a small oven-proof bowl with some water in the oven for hydration and moisture.
Score your bread, or dust it with flour, or sprinkle it with sesame seeds, and bake it at 180°C for 1 hour until it is nice and brown.