In a separate bowl, add the water and sourdough and mix. Then add the flours and mix well until there are no dry bits. Cover and leave in a warm place to autolyse for 30 minutes.
Then add the sea salt and mix well to combine. Leave for another 30 minutes.
Meanwhile weigh the sunflower seeds and place them onto a baking tray and into a preheated oven to toast. Remove and allow to cool.
During the first part of the bulk fermentation do a series of stretches and folds. 3 in total, every 30 minutes. During the second stretch and fold, add the toasted sunflower seeds. The gluten structure is delicate so be gentle when handling the dough, especially after adding the seeds.
Leave in a warm place in between the folds and then allow to rise for about another hour and a half before shaping.
Prepare the loaf tin, if it is new make sure you lightly grease it and you can also line it with a piece of baking paper until you have built up some non – stickness.
Turn the dough out onto a lightly floured work surface and pre-shape. Cover with an upturned bowl. Allow to rest for about 20 minutes, shape and place into the tin, seam side down.
Cover and allow to rise at room temperature until it just crowns the top of the tin. Or you could put it into the fridge at this point and leave overnight.
Pre heat the oven to 230C and when your dough is ready sprinkle with flour, score and bake with steam. You can add steam by using a water spray or by adding half a cup of water to a preheated tray in the oven.
If your loaf is colouring too quickly turn the oven down to 210C.
Bake for about 30 minutes or until golden brown. You can also remove the loaf from the tin and pop it back in the oven for an all round crisper crust.
Allow to cool on a wire rack for about an hour before slicing.