Place all ingredients into the Thermomix bowl and blend 10 sec/speed 6.
Tip out into an oiled bowl, cover and leave for approximately 12-16 hours or until doubled. If it is summer, this make take less time. You can do a couple of folds during this time. It is nice to feel the elasticity of the dough and get to know how it should feel when it is ready to shape.
When you are ready to form the loaf, decide which shape you will make. We used a banneton to proof the loaf again. Loads of rice flour (or fine polenta) which helps prevent stickery. Shape the loaf gently using the pull and fold technique (see the video) and allow it to rise in the banneton until bubbly and you can see that it is ready. This may take up to 4 hours or more.
Preheat your oven to as hot as it can get for at least an hour. My oven goes to 275°C which is the temperature I use in the first cooking time. You need to preheat the Dutch oven at the same time. Tip your dough out onto a piece of baking paper. Score as you wish.
Place the loaf into the heated cast iron Dutch oven using the paper and cover. Bake 25 minutes with lid on, reduce temperature to 220°C and cook further 25 minutes with the lid off. If you like a darker crust which I do, you can go for 30 minutes with the lid off.
Cool completely before slicing. (If you are disciplined enough!)