Finely slice onion. Put butter and oil in a saucepan. Melt the butter on low heat. Add onions and mix well. Cover with a lid and cook for 20 minutes on medium-low heat until onions are soft.
How to caramelize the onions: over medium heat, season the onions with sugar and salt and pepper and mix thoroughly, with the lid off, stirring constantly. Fry onions until liquid is almost gone and onions are well-browned and almost burnt. On middle-low heat saute briefly to form a brown paste. Cook for another 2-3 minutes, stirring constantly.
Gradually add the water and scrape off the cooked onion pieces from the bottom of the pot. Add broth powder, pepper (to taste), soy sauce, seasoning and bay leaf. Season with salt and pepper. Bring to a boil and simmer over low heat for 30 minutes. Lightly toast 2 slices of bread.
Remove bay leaf. Fill soup in 2 bowls. Optional: grate cheese coarsely. Sprinkle with raw onion as garnish. Put each slice of bread on the soup. Sprinkle with cheese. Serve immediately.
The recipe is very small and there is only enough soup for two, but the amount of onions is huge (more than 200g). This is not a mistake. And it is also important for the onions to be almost burned. Without this browning the color of the soup is not right. In this case, (almost) burnt is good!
This dish is also completely vegetarian. As a workaround, I have replaced soy sauce to give the onion soup a meat flavor (beef broth) that would otherwise be traditional onion soup. Additional bonus: No wine needed for this recipe.