Preheat the oven to 350 degrees. Sauté onions in the extra virgin olive oil until onions are translucent (approximately 5 minutes). Season chicken breasts with salt and pepper. Then brown one side of the chicken breasts in the pan with the onions. Flip the chicken breasts. Add the garlic cloves (unpeeled) and rosemary to the pan. Put the entire pan (I use a cast iron skillet) in the oven for 25 minutes.
Transfer chicken and seasonings to a separate dish when cooked. Place the pan back on the stove, medium heat. Add the white wine vinegar and water. Scrape the brown scraps off the pan and stir the mixture. Let the mixture cook until slightly thickened (approximately 3-4 minutes). Pour the mixture over the chicken. Enjoy!