In a Dutch oven, place steamer basket over 1 in. of water. Place a fourth of the spinach in basket. Bring water to a boil. Reduce heat to maintain a low boil; steam, covered, 3-4 minutes or just until spinach is wilted. Transfer to a colander; drain. Repeat with remaining spinach.
When spinach is cool enough to handle, squeeze dry. Coarsely chop spinach.
In clean Dutch oven, heat butter over medium-high heat. Add onions; cook and stir until tender. Stir in flour, salt and white pepper until blended; gradually whisk in milk and cream. Bring to a boil, stirring constantly; cook and stir 1-2 minutes or until thickened. Stir in cheese and spinach; heat through.
