Notes: The cornbread (homemade or from a 13-oz. mix) can be baked up to 1 day before preparing dressing. If you especially like mustard greens, use two packages. Prepare dressing through step 4 up to 1 day ahead; cover and chill. Heat, covered, in a microwave-safe container in a microwave oven on full power (100%), stirring occasionally, until hot in the center, 5 to 6 minutes. Or bake, covered, as directed in step 5 until hot, 50 to 60 minutes, then uncover to brown as directed.