Steam spinach in a sauté pan with a little water added. As soon as it is wilted, drain and make sure all water is removed. Chop spinach and set aside to cool.
Wipe out saute pan. Melt butter in pan over medium heat. Add sliced onions and sauté until onions are caramelized stirring occasionally. Reduce heat if onions are browning too quickly. When caramelized and tender remove onions from heat and cool.
Combine spinach, onions, Stonewall Kitchen Ranch Salad Dressing and sour cream. Mix until uniform and chill in refrigerator. Serve with vegetable crudites, chips or on a baked potato.