Mix flour, levain and 400g of water. Cover bowl with a plastic bag and let rest for 10-20 minutes (this is called an autolyse). Add the salt and remaining water. Scrunch the dough between your fingers, breaking up the gluten strands and incorporating the new ingredients. Scrunch until there is no excess water left in the bottom of the bowl. The dough will look like a mucilaginous bowl of oatmeal. Totally disgusting. Let sit again, covered, for 15 minutes.

Pour a tablespoon or two of olive oil around the edges of the dough and scoop the dough up from the side with one hand. Flip your palm downwards, folding the dough onto itself from the top. Rotate the bowl around and continue for about 20 seconds. Pour another light tablespoon of olive oil on top and cover and rest again for 15 minutes. 

Do this three more times over the course of 45 minutes. The dough should feel very wet but elastic and smooth, and should not tear when lightly pulled upwards. After all of your folds are complete, cover and let sit at room temperature for 3 to 4 hours. 

After this fermentation, put the dough in the refrigerator overnight, but preferably around 36 hours or more. 

When ready to bake, line a heavy baking sheet with parchment and drizzle thoroughly with olive oil. Pour the dough onto it, keeping the smooth exterior as the top surface if possible. Gently press outwards with your fingertips, but do not pull or be rough with it. The tension will lighten as it sits. Cover (I use another inverted sheet tray to do this). 

After 30 minutes, stretch the dough gently outwards into a round, about an inch thick. Cover again and let proof for about two hours.

Twenty minutes before you’re ready to bake, preheat the oven to 425 degrees. Once dough is proofed, gently dimple with greased hands to avoid air bubbles and drizzle with olive oil and salt. 

Bake for 20 minutes, or until brown spots make themselves known on the surface. Cool on a wire rack, just long enough to not burn yourself while eating.