1 cup sourdough starter
1¼ cup warm water (105°-110°)
3½ cups bread flour
1 Tbsp kosher salt
1½ tsp active dry yeast
Semolina flour for finishing
STEP 1: MIX THE DOUGH
Using a stand mixer fitted with a dough hook, combine sourdough starter and 1¼ cups warm water. Beat at medium speed until combined, about 3 min. Add flour, salt, and yeast, beating at medium speed until a soft dough forms. If the dough is too dry and crumbly, add more water 1tbsp at a time. The dough should come together as one mass and should appear shaggy and feel sticky.
STEP 2: LET IT RISE
Spray a large bowl with cooking spray. Place dough in the bowl. Cover and let stand in a warm, draft free place (75°) until doubles in size. About 1-2 hrs.
STEP 3: DEFLATE THE DOUGH/SHAPE THE BOULE
Turn risen dough out on a lightly oiled surface, and deflate it to remove any excess gas and air. Pull the 4 corners of the dough into the center pinching with your fingers to create a seal. Turn the dough over and begin to tighten the round by cupping your palms over while rotating it.
STEP 4: PROOF THE DOUGH
Line a bowl (about 6-8 inches in diameter) with a clean kitchen towel, dusted generously with flour. Place the loaf, seam side up, in the bowl. Cover and proof in a warm, draft free place (again 75°) until doubled in size, 1-2 hrs.
STEP 5: SCORE THE LOAF
Preheat oven to 450°. Turn the dough out into a cast iron dutch oven. Dust the bottom with Semolina flour and using a sharp knife (or a lame) make 3 or 4, ¼ inch deep cuts across the top of the loaf.
STEP 6: BAKE THE LOAF
Cover and bake for 35 minutes. Increase oven temp to 475°, remove the lid and continue baking until loaf is browned (10-15 min) Turn onto a wire rack, let cool completely before slicing.