Combine first 3 ingredients in a medium saucepan, and place over medium heat until margarine melts. Cool slightly (to 120° to 130°). Combine 2 cups cornmeal and yeast in a large bowl, and add milk mixture, stirring well with a whisk. Lightly spoon flour into dry measuring cups, and level with a knife. Add flour and salt to cornmeal mixture, and stir until a soft dough forms. Turn dough out onto a lightly floured surface; knead 3 or 4 times. Cover and let rest 15 minutes. Knead dough until smooth and elastic (about 8 minutes).
Place dough in a large bowl coated with cooking spray, turning to coat top. Cover and let rise in a warm place (85°), free from drafts, 50 minutes or until doubled in size. Punch dough down; divide dough in half. Coat 2 (9-inch) pie plates or cake pans with cooking spray; dust each with 1 1/2 teaspoons cornmeal. Working with 1 portion at a time (cover remaining half to keep from drying), shape dough into a 7-inch round. Place round, seam side down, in prepared plate. Repeat procedure with remaining half of dough. Cover and let rise 20 minutes or until doubled in size.
Preheat oven to 350°.
Lightly score rounds in a spiral pattern using a sharp knife. Bake at 350° for 45 minutes or until rounds sound hollow when tapped. Remove from plates; cool on wire racks.