Start by feeding your starter then leave at room temperature until it is at its’ peak, just before it starts to fall. This should take around 5 hours.
An hour before your starter is ready, in a bowl, mix together both the flours, 300g water & the olive oil. Cover & leave for 1 hour.
Next, make the porridge. Brown the butter over a medium heat then add the oats & cook in the butter for 2-3 minutes. Transfer to a low heat, add the water & malt extract & cook until thick & creamy but still slightly wet. Roughly 5-8 minutes.Transfer porridge to a lined baking tray & leave to cool to room temperature. Next, add the starter to the autolysed dough. Using your hand, squeeze the starter into the dough then transfer to a work surface & “slap & fold” until combined. Roughly 2-3 minutes. Return dough to bowl, cover & leave for 1 hour. Tip the salt & remaining 30g of water over the dough & squeeze the salt into the dough until combined.Break the porridge up into the dough & use your hands to mix it into the dough. Transfer the dough to a clean work surface & “slap & fold” for roughly 10 minutes or until the dough comes together & is less sticky. Coil fold the dough every 30 minutes until the dough passes the windowpane test. (I find that 4-6 coil folds tends to do the trick).Leave undisturbed for the remainder of the bulk ferment (2-4 hours).The bulk ferment starts as soon as the starter is added to the dough & will take anywhere from 4-10 hours (depending on room temperature, dough hydration & flour used). When the dough has finished fermenting, it will have increased in volume by roughly 20-30%, the top will be domed & you will see lots of tiny bubbles in the dough. Once the bulk ferment has finished, gently tip the dough out onto a clean work surface, with the help of a dough scraper.
Using a metal bench knife & a hand dipped in water, gently work the dough into a round shape. (Don’t shape it too tightly as this could damage the gluten in the dough.) Dust the top of the dough with rice flour & leave to rest for 20 minutes.
Lightly dust a banneton with rice flour.Using a bench knife, gently loosen the dough from the work surface then carefully flip the dough over.Pull the bottom side of the dough up & fold it into the middle. Press down lightly to make sure the dough has stuck (press down lightly with every fold).Now take the left side, stretch it slightly & fold it roughly ¾ to the right.Next, stretch the right side slightly & fold over the left side.Take the top side, stretch it away from you then fold it into the centre of the dough.Now “stitch” the sourdough. Starting at the top, pinch a small amount of dough from both the left & right sides. Fold the dough from the right side over the centre, followed by the left side. Repeat this process in the middle section of dough then the bottom section. (Imagine the pattern of a laced up shoe).Finally, starting from the bottom to the top, carefully roll the dough over itself. Use a bench knife to gently pull the shaped dough towards you, dragging the bottom of the dough on the work surface. This seals the underneath & helps create tension.Dust the surface of the dough with rice flour, turn the dough upside down (so that the dough is seam side up) & place into the banneton. Cover the top of the banneton with clingfilm & place into a fridge for 12-15 hours. The longer the dough is left in the fridge, the more sour the final loaf will be. Place your casserole dish or Dutch oven into your oven & preheat to 230°c for 1 hour.The casserole dish I use can be used upside down so that the dough sits on the lid & the casserole dish itself acts as a lid. This means there’s plenty of room for oven spring.Whilst your oven is preheating, place the banneton with the dough in into a freezer. Remove the banneton from the freezer. Place your prepared piece of parchment over the top of the banneton then a chopping board/flat tray. Flip the banneton/chopping board over so that the dough is now sat seam side down on the parchment.To score the dough, hold the lame so that the razor is at an angle to the dough. Between 30° & 45°. Starting at the top end of the dough, slash the dough all the way to the bottom end. The score should be off centre to the right & at least 1cm deep. For best results, try to score in one cut. Dipping the razor in water before scoring helps produce a clean cut.Using the parchment, slide the dough into the preheated casserole dish. Spray generously with cold water & place the lid on the dish. Bake in the preheated oven, covered for 25 minutes then remove the lid & bake for a further 20-25 minutes, until the loaf is a deep, brown colour. For the best flavour, the dough should be fairly dark but not burnt.
Transfer the dough to a wire rack & leave to cool completely before slicing. This will take a couple of hours.