3   small heads Bibb lettuce, cleaned and torn into bite-size pieces
1 1/2 lb fresh spinach, cleaned and torn into bite-size pieces
3   oranges, peeled, sectioned, and seeded
3/4   medium red onion, sliced and separated into rings
3/4 cup walnuts, coarsely chopped
3 teaspoon butter

Sweet-and Sour Dressing:
1 1/2 cups vegetable oil
3/4 cup vinegar
3/4 cup sugar
1 1/2 teaspoons salt
1 1/2 teaspoon celery seed
1 1/2 teaspoons dry mustard
1 1/2 teaspoons paprika
1 1/2 teaspoons grated onion