This was posted a while back in the Recipes Collection:

 

from To Market, To Market...
A Collection of Kentucky Recipes

6 large white onions
6 slices of bacon
1 can (10-3/4 ounces) cream of mushroom soup
1 package (10 ounces) frozen chopped spinach,
  cooked and drained
1 Tablespoon brown sugar
1 Tablespoon vinegar

Procedure

TO PREPARE:

1.  Cut off tops of onions.  Scoop out, leaving last two
    rings intact.  Chop onion centers.
2.  Fry bacon until crisp; crumble.
3.  Using one-half of the chopped onion, sauté in a little
    of the bacon drippings until tender.
4.  Add soup, spinach, brown sugar, vinegar, and bacon to
    sautéed onions.  Blend well.
5.  Fill onions shells with spinach mixture.  Place filled
    onions shells on baking sheet and cover with foil.
6.  Bake at 375 degrees 30 to 45 minutes until tender.

SERVINGS: 6

Serving Information

• Serves: 6