Add 1 cup flour, yeast, sugar and salt to stand mixer bowl; whisk to combine. Add sourdough starter and water; mix with paddle attachment for 4 minutes on medium speed.
Switch to dough hook attachment. Gradually add remaining flour and knead until smooth and elastic, about 5 to 7 minutes.(NOTE: For hand mixing: following above steps, mix ingredients in large mixing bowl using a wooden spoon or dough whisk. Knead on floured surface until smooth and elastic.)
Place dough in lightly oiled bowl and turnto grease top. Cover; let rise until indentation remains after poking doughwith finger down to second knuckle, about an hour.
Turn dough onto lightly floured surface; punch down to remove air bubbles. Roll or pat into a 12x5-inch rectangle. Starting with shorter side, roll up tightly, pressing dough into roll. Pinch edges and taper ends to seal. Place on baking sheet that is lined with parchment paper or silicone mat; sprinkle top of loaf with cornmeal. Cover; let rise until indentation remains after touching.
Preheat oven to 400°F.
With very sharp knife or bread lame, make 2 or 3 diagonal slashes across top of loaf. Spray or brush loaf with cold water. (For a crisper crust, spray or brush loaf with cold water several times during the first 12 minutes of baking.)
Bake for 30 to 35 minutes. Remove from cookie sheet; cool on wire rack.