Combine sugar, shortening, and salt in a large mixing bowl; add Sourdough Starter, and stir until sugar dissolves.
Gradually add flour, stirring until dough leaves sides of bowl. Turn dough out onto a heavily floured surface; knead 10 minutes or until smooth and elastic. Place dough in a greased bowl, turning to grease top. Cover and let rise in a warm place (85°), free from drafts, 1 hour or until doubled in bulk (dough will be sticky). Punch dough down, and let rest 5 minutes. Turn dough out onto a floured surface; divide in half.
Grease a baking sheet; sprinkle with cornmeal. Set aside.
Roll each half into a 12- x 10- inch rectangle. Roll up jellyroll fashion, beginning at wide edge. Place dough, seam side down, on baking sheet; turn edges under. Cover and repeat rising procedure 25 minutes or until doubled in bulk.
Cut several diagonal slashes, 3/4-inch deep, in top of each loaf. Bake at 400° for 30 minutes or until loaves sound hollow when tapped. Remove to wire racks to cool.