1. Activate Your Sourdough Starter: The night before you plan to mix your dough, feed your sourdough starter. Combine 50 grams of your unfed starter with 50 grams of warm water and 50 grams of bread flour in a clean jar. Stir well, cover loosely, and let it sit at room temperature for 8-12 hours, until it’s bubbly, has doubled in size, and passes the float test (a small spoonful floats in water).

2. Mix the Dough (Autolyse): In a large mixing bowl, combine the 350 grams of warm water with 100 grams of your active sourdough starter. Stir until the starter is mostly dissolved. Add the 500 grams of bread flour and mix with a Danish dough whisk or your hands until no dry spots remain and a shaggy dough forms. Cover the bowl with a damp towel or plastic wrap and let it rest for 30 minutes (this is called autolyse, which helps the flour hydrate).

3. Incorporate the Salt: After the autolyse, sprinkle the 10 grams of fine sea salt over the dough. With wet hands, gently squeeze and fold the dough for 2-3 minutes to fully incorporate the salt. The dough will feel sticky at first but will start to come together.

4. Perform Stretch and Folds: Over the next 2-3 hours, perform a series of “stretch and folds.” Every 30 minutes, with wet hands, grab a portion of the dough from one side, stretch it upwards, and fold it over to the opposite side. Rotate the bowl and repeat this process 3-4 times until all sides have been stretched and folded. Do this for a total of 4-6 sets. You’ll notice the dough becoming smoother, stronger, and more elastic with each set.

5. Shape the Dough: Lightly flour your work surface. Gently turn the dough out onto the surface. Carefully pre-shape the dough into a round or oval by gently pulling the edges towards the center to create tension on the surface. Let it rest for 20 minutes, uncovered. Then, perform the final shaping: lightly flour the top of the dough, flip it over, and gently stretch out the edges. Fold the top third down, the bottom third up, and then fold in the sides, creating a tight, round or oval shape.

6. Cold Proofing: Lightly dust a banneton (proofing basket) or a bowl lined with a floured kitchen towel generously with rice flour. Carefully transfer the shaped dough, seam-side up, into the banneton. Cover the banneton with a plastic bag or plastic wrap and refrigerate for 8-12 hours, or up to 24 hours. Cold proofing develops flavor and makes the dough easier to handle.

7. Preheat Oven and Baking Steel: About 45-60 minutes before you’re ready to bake, place your baking steel on the middle rack of your oven. Preheat the oven to 500 F (260 C) with the baking steel inside. This long preheat ensures the steel is fully saturated with heat.

8. Bake the Loaf: Carefully remove the cold dough from the refrigerator. Gently invert the dough onto a piece of parchment paper. Score the top of the dough with a sharp razor blade or knife (a single long slash or a decorative pattern). Carefully slide the parchment paper with the dough onto the preheated baking steel. Immediately reduce the oven temperature to 450 F (230 C). Bake for 20 minutes. After 20 minutes, carefully remove the parchment paper from under the loaf (using tongs is helpful). Continue baking for another 15-20 minutes, or until the crust is deep golden brown and the internal temperature reaches 200-210 F (93-99 C).

9. Cool Completely: Once baked, transfer the loaf to a wire rack and let it cool completely for at least 1-2 hours before slicing. This is crucial for the crumb to set and for the flavor to fully develop. Slicing too early can result in a gummy texture.