This is a delicious side dish that goes well with beef or chicken. Many times I have used bacon instead of the pancetta. I also use 2 cloves of garlic. This is adapted from Cooks Illustrated, Jan. 1996 edition. Hope you enjoy!
Heat oil in medium oven-proof skillet over medium heat. Add pancetta (or bacon) cook until crisp, about 4 minutes. Add garlic; sauté until fragrant, about 1 minute. Add celery and carrot; sauté to soften slightly, about 2 minutes.
Increase heat to high. Add onions; sauté until spotty brown, being careful not to burn other ingredients, about 2 minutes.
Add wine; cook to reduce slightly, about 30 seconds. Add herbs and stock; bring to simmer.
Cover skillet and braise vegetables in oven 10 minutes. Uncover skillet and continue to braise vegetables until onions are soft but not mushy, about 10 minutes longer. Season to taste with salt and pepper.