Sourdough Bread
["1 pkg. dry yeast", "3 1/2 c. warm water, divided", "7 c. all-purpose flour, divided", "1/4 c. nonfat dry milk", "2 Tbsp. margarine, melted", "2 Tbsp. sugar", "2 tsp. salt", "cornmeal"]
["Before starting your bread, rinse a 2 1/2-quart saucepan with 1 teaspoon soda in 1 cup boiling water."]
["yeast", "warm water", "all-purpose flour", "nonfat dry milk", "margarine", "sugar", "salt", "cornmeal"]