Mix together ripe/active sourdough starter with all-purpose or bread flour and water. Cover loosely and let sit 10-12 hours at 78-80°F until doubled, bubbly & peaked.

To a large bowl, mix together ripe levain with water. Add salt and bread flour. Mix together using a dough whisk or spoon until a wet and sticky dough forms and the ingredients are fully combined. Cover and let rest for 30 minutes.

After the dough has rested, perform a series of 'stretch and folds' over the next 1 ½ hours.

After 30 minutes, perform your first set of stretch and folds. Cover the dough and let rest for 30 minutes.

After 30 minutes, grate the cold butter. Put half of the grated butter on top of the dough. Stretch and fold the dough again, incorporating the flakes of butter into the dough. Cover and let rest for 30 minutes.

30 minutes later, add the rest of the butter to the top of the dough. Stretch and fold again. Cover and let rest for 30 minutes.

After 30 minutes do your final set of stretch and folds. Cover the dough and let rise for 6-7 more hours.

Tip the bowl upside down, allowing the dough to fall onto a clean counter surface. Wet your hands and the bench knife if needed and push the bench knife under the dough on one side and your free hand on the other side to tuck the dough under itself.

Let the dough rest uncovered for about 30 minutes at room temperature.

Prepare a bowl or banneton. Shape the dough and place it into a lined bowl.

Cover the dough and refrigerate overnight or up to 12-18 hours.

Preheat a Dutch oven to 450°F for 20 minutes. Remove the covering and flip the dough onto parchment paper.

Use a very sharp knife or bread lame to score the dough.

Carefully remove the Dutch oven from the oven. Place your bread into the Dutch oven and lower the temperature to 425°F. Bake for 25 minutes covered and 20 minutes uncovered.