Cook Onions: Bring a large Dutch Oven to medium-high heat. Add butter and olive oil to the pan. Let butter melt; swirl to coat the pan. Add shallot and onions. Cook on medium heat until softened, about 15 minutes. Increase to medium-high and add additional butter or olive oil, if needed (if pan seems dry). Cook another 30 minutes until caramelized, moving around fairly constantly. Add sugar and stir to combine to really get some extra caramelization. 

Deglaze Pan: Deglaze pan by adding wine and scraping up any bits that are stuck to the bottom of the pan. The onions should resemble almost a jam-like texture at this point. Add garlic and stir to combine. 

Finish Soup: Add flour and stir to combine. Slowly add broth, approx. 1/4 cup at a time, stirring constantly. Add Beef Broth Concentrate, worsteshire, balsamic vinegar, lemon zest, soy sauce, pepper, pinch of salt and herb bundle. Cover and let simmer 20-30 minutes. 

Baguettes: Meanwhile, preheat oven to 450 degrees F. Place sliced baguettes on baking sheet. Brush with olive oil. Place in oven, middle rack, until browned, approx. 5 minutes (watch closely). 

Taste + Adjust: Taste soup and add additional salt, as desired.

Broil: Ladle soup into 4 small bowls or 2 big bowls. Place 2 baguettes on top. Cover with gruyere and parmesan cheese. Place under the broiler until cheese melted and bubbly (watch closely and I would recommend dropping the top rack so it isn't directly under the broiler). 

Serve: Remove and let cool slightly before serving. Garnish with fresh chopped parsley.