In a large pot, melt the butter on high heat. Avoid browning the butter by adding onions before the butter is completely melted. Season with kosher salt to draw out the moisture in the onions. Stir frequently and cook for about 15 minutes. You may notice that the onions have become translucent and some water has leached out. Keep the temperature high and the stirring frequent until the moisture has evaporated and the onions are starting to colour/caramelize and stick to the bottom of the pot. (Brown colour is good, black is too far, if the onions get too dark the soup will be bitter. You may add some water to deglaze the pot if the onions colour accidentally).

Reduce the heat to medium-low and continue to caramelize for at least 1 hour. Stir occasionally and add small amounts of water (1 Tbsp.) if the onions stick to the pot.

Once the onions are at a deep brown colour and all of the moisture has evaporated. Add garlic and cook for 1 minute. Sift in the flour and stir aggressively to avoid lumps. Cook for an additional 3-4 minutes.

Add the red wine and allow the liquid to lift all the sticky onions and starch from the bottom of the pot. Add the beef stock and herbs and simmer for 1-1 ½ hours.

After the soup has simmered, add the sherry vinegar and taste the soup. Add additional salt if needed and remove the bay leaves.

Using oven-proof bowls or a large casserole dish, ladle soup into dishes. Cover with the bread croutons and sprinkle with cheese. Put under the broiler for 5-8 minutes or until the cheese bubbles and is slightly browned. Carefully Take out of the oven and sprinkle chopped herbs and grated parmesan. Enjoy!!