In a large pot over medium/low heat, heat olive oil and butter. Once the butter is melted, stir in the onions and coat with oil and butter.

Cover and cook for 20 minutes, checking occasionally.

Turn up the heat to medium/high and add salt & sugar. Stir and keep cooking until onions are brown and caramelized (the bottom of the pan will develop some browning, its very important.)

Stir in flour one tablespoon at a time and cook for about 30 seconds.

Add 1 cup of the beef stock, use a whisk to scrape the bottom of the pan.

Add the remaining 5 cups of beef stock, sage, bay leaf and bring to a boil, reduce heat and simmer, uncovered for about 40 minutes.

Add balsamic vinegar, cook for another 2-3 minutes.

Serve in bowls and add your shredded provolone cheese to top!