Mix 2 cups of bread flour, 1 cup of warm water, and 0.25 teaspoons of yeast in a medium bowl until it resembles dough. Cover with plastic wrap and let sit for 24 hours to develop flavor.

Add the remaining 2 cups of bread flour, 0.25 teaspoons of yeast, 1.25 cups of warm water, and 2 teaspoons of salt to the sponge. Mix with a stand mixer on low until combined, then let rest for 20 minutes.

After resting, add the sponge and salt to the dough. Mix on medium low for 8 minutes until elastic. Turn out onto floured surface and shape into a ball.

Place dough in a greased bowl, cover, and let rise until doubled, about 1 hour.

Punch down the dough, shape into a loaf, and place on a parchment-lined baking sheet. Cover and let rise until doubled, 60 to 90 minutes.

Preheat oven to 500°F with baking stone inside for 30 minutes. Score the top of the loaf diagonally with a razor blade.

Carefully slide the loaf and parchment onto the hot baking stone. Bake for 10 minutes, then reduce temperature to 400°F and bake for an additional 30-35 minutes until deep golden brown. Cool on wire rack.