Heat a large saucepan over medium-high heat and add the chopped pancetta. Cook until golden brown. Remove the pancetta with a slotted spoon and drain on a paper towel.
Discard all but 1 teaspoon of the pancetta, add 1 teaspoon olive oil and set the saucepan over medium-high heat.
Add the garlic and cook until fragrant, about 1 minute.
Add onions and endive and cook, stirring occasionally, until the onions are very soft and light golden brown.
Reduce heat to medium heat and cook until the onions and endive are golden brown, about 15 minutes.
Add the wine and balsamic vinegar and stir until most of the liquid is absorbed, about 3 minutes. Add the beef broth, bring to a boil, then reduce heat and simmer about 20 minutes. Stir in the cooked pancetta.
Place the baguette slices on a cookie sheet and toast in a 350 degree oven for about 5 minutes.
Preheat the broiler. Ladle the soup into ovenproof bowls and top each with 1 baguette slices and 1 tablespoon cheese. Broil until the cheese is bubbling and slightly brown. Serve.