Peel and slice onions.
Add oil to pan and sauté onions until they soften - about 20 minutes.
Increase the heat, add butter and brown the onions - about 20-40 minutes.
Sprinkle with sugar and finish caramelising onions, then add garlic.
Deglaze the pot with vermouth, making sure to scrape down all the brown bits.
Add stock, bay leaves and thyme and simmer for 30 minutes. Season to taste.
Preheat oven and line tray with baking paper.
Slice Paris Sour Dough into generous chunks. Toast one side till golden and then flip over, add cheese and toast until golden.
To serve, ladle soup into bowls and top with Paris sourdough cheese floats.
