Prepare the levain. Mix the sourdough starter, flour, and water in a clean jar. Cover loosely and let ferment at room temperature until doubled in volume and full of bubbles, 4 to 6 hours.

Autolyse the flours. Combine the bread flour and whole wheat flour with water in a large bowl. Mix until no dry flour remains. Cover and rest 30 to 60 minutes to hydrate fully.

Mix the dough. Add the levain, salt, cardamom, and honey to the autolysed mixture. Squeeze and fold with wet hands until fully incorporated, 5 to 8 minutes. Target dough temperature of 76 to 78°F (24 to 26°C).

Bulk fermentation. Rest 30 minutes, then perform 4 to 6 sets of stretch and folds every 30 to 45 minutes for the first 2 to 2.5 hours. If using raisins, fold them in during the first couple of sets. Continue bulk fermentation for a total of 4 to 7 hours until the dough increases 50 to 75 percent in volume and jiggles slightly when the bowl is shaken.

Pre-shape and bench rest. Turn the dough onto a lightly floured surface. Fold the edges to the center to form a loose round. Flip seam side down and rest 20 to 30 minutes.

Final shaping. Shape into a boule or batard, creating surface tension. Place seam side up in a floured proofing basket lined with a tea towel.

Final proof. Cover and proof at room temperature for 1 to 2 hours, or retard in the refrigerator overnight for 8 to 16 hours for deeper flavor. Ready when a gentle finger press springs back slowly.

Bake. Preheat the oven to 450°F (232°C) with a Dutch oven inside for 45 to 60 minutes. Score the loaf. Bake covered for 20 minutes, then uncovered at 425°F (218°C) for 20 to 25 minutes until deep golden, internal temperature 205 to 210°F (96 to 99°C).

Cool completely. Cool on a wire rack for at least 2 hours before slicing to preserve the crumb structure.