Turn the Instant Pot on Sauté mode and heat butter and oil.

Add onions, salt, sugar and cook for 20-25 minutes stirring every 5 mins until onions turn golden brown.

Press Cancel. Add wine and deglaze the pot removing all browning from the pot. Cook for 2-3 minutes.

Add bay leaf, thyme, black pepper, Worcestershire sauce, and 2½ cups of broth. Secure the lid and Pressure Cook (Hi) for 6 minutes followed by Quick Release.

Open the Instant Pot, remove the bay leaf and discard. Mix all-purpose flour in the remaining half cup of broth and slowly stir in the soup. Cook for 5 minutes as the soup thickens.

Preheat oven to broil. Cut baguette into bite-sized pieces and toast until golden brown (5 to 7 minutes).

Add ¾ cup of soup to an oven-safe bowl. Add toasted bread pieces and top with shredded Gruyere cheese and Swiss cheese slices.