Mix 50g active sourdough starter with 100g water (80-85°F) in a clean jar.

Add 100g bread flour and stir until combined. The mixture will be thick and paste-like.

Cover loosely and let sit at room temperature overnight (8-10 hours). It should be bubbly, domed, and doubled by morning.

In a large bowl, add 350g water (80-85°F) and dissolve all of your levain into it. It should break apart easily.

Add 500g bread flour and mix with your hands until no dry flour remains. The dough will look shaggy and rough.

Cover and let rest for 45 minutes. This autolyse develops gluten without effort.

Sprinkle 10g salt over the dough.

Pinch and fold the dough repeatedly for about 5 minutes until the salt is fully incorporated and the dough starts to tighten up.

Cover and rest for 30 minutes before starting folds.

Wet your hand, grab one side of the dough, stretch it up, and fold it over itself. Rotate the bowl 90 degrees and repeat 4 times total.

Before adding inclusions, make sure the dough is strong enough. It should stretch without tearing. If it tears, do another set of folds and wait 30 minutes.

Add half the shredded cheese, cubed cheese, and jalapeños. Fold them in gently with another round of stretch and folds. Rest 30 minutes.

Add the remaining cheese and jalapeños. Fold in with final stretch and folds. The dough should feel smooth, strong, and slightly puffy.

Cover and let ferment at room temperature (75-78°F). Watch for 50-75% volume increase, visible bubbles, and dome formation.

The dough is ready when it's grown 50-75%, looks puffy with bubbles on the surface, and springs back slowly when poked.

Turn dough out onto a lightly floured surface. Preshape into a round by pulling edges toward the center, creating tension on the surface.

Let rest 20 minutes uncovered (bench rest). This relaxes the gluten for final shaping.

Flip the dough so smooth side is down. Fold edges to center again, creating a tight ball. Flip over and drag across the counter using a bench scraper to build surface tension.

Place seam-side up in a well-floured banneton. Some cheese may poke out—that's perfectly fine.

Cover the banneton with plastic wrap or a shower cap. Let rest at room temperature for 1 hour.

Transfer to refrigerator for 8-24 hours. The longer the cold retard, the more complex the flavor.

When ready to bake, preheat your oven to 475°F (245°C) with your Dutch oven inside for at least 45 minutes.

Turn loaf out onto parchment paper. Scoring the top with a lame or sharp knife—one deep slash works great. The cheese may fight your blade.

Carefully remove hot Dutch oven, lower in the loaf (parchment and all), and cover with lid.

Bake covered for 20 minutes. The trapped steam allows maximum oven spring.

Remove lid and continue baking 15-20 minutes until deep golden brown with caramelized cheese on the crust. Internal temp should reach 200-205°F.

Transfer to wire rack and cool for at least 1 hour before slicing. The crumb is still setting inside.

After bulk fermentation, gently turn the dough onto a lightly floured surface.

Pull edges toward the center, creating tension on the surface. Let rest 20 minutes.

Flip smooth-side down, fold edges to center, flip over, and drag across counter with bench scraper to build surface tension.

Place seam-side up in a well-floured banneton. The seam becomes the bottom after flipping.

Remove the dough from the fridge, transfer it to parchment paper, and scoring the top using a lame or sharp knife.

Using the parchment, carefully lower the dough into the preheated baking vessel.

Cover and bake for 20 minutes. The lid traps steam from the dough itself—no additional water needed.

Remove the lid and bake for 15-20 minutes more until the cheese is caramelized and the crust is deep golden brown.

Let the loaf cool for at least 1 hour before slicing. The crumb is still setting inside.

Preheat oven to 475°F (245°C) with a baking stone or sheet on the middle rack and an empty cast iron pan or steam tray on the bottom rack. Preheat for at least 45 minutes.

Remove the dough from the fridge, transfer it to parchment paper, and scoring the top using a lame or sharp knife.

Slide the loaf (on parchment) onto the hot stone or sheet. Immediately pour 1 cup of boiling water into the steam pan and close the oven door quickly. You can also spray the oven walls with water.

Bake with steam for 20 minutes. Keep the door closed to trap moisture.

Carefully remove the steam pan (use oven mitts!) or crack the oven door to vent steam. Bake for another 15-20 minutes until the cheese is caramelized and internal temp reaches 200-205°F.

Transfer to a wire rack and cool for at least 1 hour before slicing.