Levain

• 3 tablespoons (1 1/2 ounces/40 grams) warm water (90°F to 100°F)
• 2 tablespoons (1 ounce/30 grams) mature sourdough starter
• 1/3 cup (about 1 1/4 ounces/40 grams) bread flour

Dough

• 1 1/2 cups (12 ounces/345 grams) warm water, divided
• Levain (see above)
• 4 cups (about 17 ounces/485 grams) bread flour, plus more for dusting and work surface
• 1 tablespoon (1/4 ounce/9 grams) kosher salt
• Wheat germ or white rice flour, for dusting