Feed. The night before baking, feed your starter so it's active and bubbly in the morning.
Mix. In a large bowl, combine the water and active starter. Add flour and mix until no dry flour remains. Cover and rest for 30 minutes.
Salt. Add salt and mix until well combined. The dough will feel slightly sticky but should clear the sides of the bowl.
Fold. Over the next 2 hours, perform 4 sets of stretch and folds 30 minutes apart. Keep the dough covered between folds.
Rise. Let the dough rise at room temperature for 4-6 hours until doubled and bubbly.
Shape. Turn the dough onto a lightly floured surface. Gently shape it into a round shape by folding the edges under. Place seam-side-up in a flour-dusted bowl lined with a clean kitchen towel.
Chill. Cover and refrigerate overnight (8-14 hours).
Prepare. Preheat oven to 450°F with Dutch oven inside. Line a sheet of parchment with cornmeal.
Transfer. Turn the cold dough onto the prepared parchment. Dust the top with flour and slash with a sharp knife.
Bake. Carefully lower the dough with the parchment into the hot Dutch oven. Cover and bake for 20 minutes. Remove the lid and bake for 15-20 minutes more until it is deep golden brown.
Cool. Cool completely on a wire rack before slicing.