1. In a large saucepan over medium heat, cook the pancetta until it is golden. Transfer it to a plate using a slotted spoon.
2. Return the saucepan to medium heat. Add the olive oil and onions, then cook, covered but stirring occasionally, until very soft, about 20 minutes. Remove the cover and cook, stirring frequently, for another 35 to 45 minutes, or until the onions are golden brown and caramelized. Add the wine and boil until it is reduced by half. Add the broth and simmer for another 20 minutes.
3. Bring a large saucepan of salted water to a low simmer. Add the vinegar.
4. Crack each egg into a small glass. One at a time, gently and slowly pour each egg into the simmering water, bringing the lip of the glass right down to the water so that the egg slides in. Depending on the size of your pan, you may need to cook them in 2 batches. Cook for 4 minutes, then use a slotted spoon to lift each egg out (letting excess water drip away).
5. To serve, ladle the soup into 4 bowls. Top each with a poached egg, sprinkle with some of the cheese, some of the pancetta and pepper to taste. Serve each portion with 2 toasts on the side.
Nutrition information per serving: 710 calories; 250 calories from fat (35 percent of total calories); 28 g fat (8 g saturated; 0 g trans fats); 200 mg cholesterol; 73 g carbohydrate; 8 g fiber; 19 g sugar; 31 g protein; 1200 mg sodium.