In the bowl of a stand mixer, combine the sponge ingredients. Whisk thoroughly to combine.
Cover the sponge ingredients with the final dough ingredients and don't stir together. Cover the bowl with plastic and let sit for 4 hours. The sponge will be bubbling through the other ingredients after the 4 hours.
Attach a dough hook. Mixer slowly for a few seconds to prevent flour flying everywhere. Then increase the speed to medium and knead for 10-15 minutes. The dough should be smooth, elastic and springy. Cover and let rise for 1.5-2 hours, until doubled.
Scrape dough onto a lightly floured work surface, and shape into a ball. Cover with plastic and let rise again for 1 hour.
Flatten the dough ball and fold into thirds. Rotate 90 degrees, and fold into thirds again. Roll the folded dough into a log shape, and press the seem to seal. Set the log, seem side down onto parchment paper dusted with flour or corn meal. Cover and let rise for about an hour. Pre heat your oven to 450F, with a Dutch oven inside it to also pre heat.
Carefully transfer the risen log into the Dutch oven. Slash the top with a sharp knife or a bread lame. Put on the lid. Bake with the lid on for about 15 minutes. Then reduce the heat to 400F and bake for ~35 minutes. Remove the lid for the last 10 minutes. The loaf is ready when it's a deep brown, and sounds hollow when tapped on the bottom.
Cool on a wire rack completely before slicing. Store in the fridge for 2 weeks on in the freezer for up to 2 months.