Tips: To Make Ahead: Prepare as directed through step 2. Place in a 2- to 2-1/2-quart au gratin or baking dish. Cover and chill up to 24 hours. Preheat oven to 325 degrees Fahrenheit. Bake casserole, covered, for 60 to 70 minutes or until heated through. (For safety reasons, do not make ahead if planning to use for stuffing a turkey.)
To dry whole-grain bread: Cut enough slices of whole-grain bread into 1/2-inch cubes to equal 8 cups (10 to 12 slices). Spread out in a shallow baking pan. Bake, uncovered, at 300 degrees Fahrenheit for about 15 minutes or until dry and crisp, stirring twice. Cool. You should have about 6 cups dried bread cubes.