Green Beans and carmalized onions

4 strips bacon
2 large onions- cut lenthwise into 1/2 inch thick wedges
2 lbs green beans (fresh, trimmed)
3 T cider vinegar
4 1/2 tsp brown sugar
1/4 tsp salt
1/4 tsp pepper

In a large skillet, cook bacon over medium heat until crisp. Remove to paper towls. Drain. Reserve 2 T drippings. Crumble bacon and set aside. In the drippings cook onions over medium- low heat until tender and golden brown, about 50 minutes.
Meanwhile place the beans in a large saucepan and cover with water; bring to a boil. Cook, uncovered, for 8-10 minutes or until crisp-tender. Drain. Stir the vinegar and brown sugar into the onions; add beans. Cook uncovered over medium heat for 1 minute. Add bacon. Toss gently. Season with salt and pepper.