Mix the Dough (Separately): In one bowl, mix flour, water, salt, starter, and turmeric. In another bowl, mix flour, water, salt, starter, and black pepper. Cover both bowls and let rest for 30 minutes.
First and Second Stretch & Folds (Separate Doughs): Perform two sets of stretch and folds, one every 30 minutes, keeping the turmeric and black pepper doughs separate. To do a stretch and fold, wet your hands, grab one side of the dough, stretch it up, and fold it over. Rotate the bowl and repeat on all four sides.
Combine the Doughs (During Third Stretch & Fold): On the third stretch and fold, gently combine both doughs in one bowl by placing one on top of the other. Perform the stretch and folds as usual, folding the two doughs together to create a marbled effect. Be careful not to overmix to keep the colors distinct. Let the dough rest for another 30 minutes.
Bulk Fermentation: Cover and let the dough ferment at room temperature for 4–6 hours, or until it has increased in size and looks puffy.
Shaping the Dough: Lightly flour a surface and turn out the dough. Shape it into a round or oval shape. Place the shaped dough into a floured banneton or a bowl lined with a cloth.
Second Rise (Proofing): Let the dough proof for 1–3 hours at room temperature until slightly puffy.
Bake: Preheat the oven to 240°C (465°F) with a Dutch oven inside for 30 minutes. Transfer the dough onto parchment paper and place it in the hot Dutch oven. Cover with the lid and bake for 30 minutes. Lower the oven temperature to 230°C (450°F), remove the lid, and bake uncovered for 10 more minutes. Let the bread cool completely on a wire rack before slicing.
Notes
If you want the dough colors to mix more or less, experiment with adding one dough to the other during different rounds of stretch and folds. Mixing them together sooner will mix them more, while mixing them together later will give more of a marbled effect.
Don’t over-mix the doughs, as keeping them distinct creates the marbled effect.
Use finely ground black pepper because It distributes more evenly in the dough.
Keep in mind that proofing time varies on your kitchen temperature, so don't be afraid to go by the dough, not by the clock!