In a large pot over medium high heat, add butter and olive oil
Add in onions and caramelize for about 30 minutes until dark brown. This process will take a while so be patient!
Once the onions are caramelized, pour in white wine and sherry to "deglaze" the pan
Reduce the liquid by 2/3
Once the wine is reduced, pour in beef broth
Add in thyme, bay leaves, and season with salt and pepper to taste
Cover the pot and let simmer for 30 minutes
TASTE IT!
Preheat oven broiler
Lay out french bread slices on a baking sheet and drizzle with olive oil
Toast the bread in the oven for about 5 minutes until golden brown and set aside
In an oven save bowl (I used mini enamel pots), fill with soup about 3/4 of the way up
Top with 2 or 3 baguette slices and cover with 2 slices of Gruyere cheese
Add about 2 tablespoons of freshly grated parmesan cheese on to of that
Place on a baking sheet just in case the soup bubbles over.
Place in broiler and melt the cheese until golden and bubbly (Watch it closely!)
Let cool for a few minutes then dig in!