Peel and slice onions.  Heat a large dutch oven to medium heat.  Add 3 tablespoons butter and 1 tablespoon olive oil (I use Rosemary Olive Oil from our Shop).  When melted, add onions and stir.  Continue to cook, stirring occasionally for about 15 minutes.

Continue cooking uncovered for about 15 minutes more and then add sugar and 1/2 teaspoon salt.  Continue cooking for another 10-15 minutes or until onions are deep golden brown.

Add remaining tablespoon butter, flour, and garlic and stir for about a minute.  Slowly add beef broth, stopping after the first couple cups to really scrape down sides and bottom of pan and whisk broth smooth.  Continue adding remaining broth, along with black pepper and thyme and bring soup to a simmer.  Simmer uncovered for 20-30 minutes.

While soup is simmering, prepare bread. Preheat oven to 400 degrees. Slice baguette and place on baking sheet. Drizzle with olive oil and then bake for about 10 minutes or until toasted and very lightly golden.

Turn heat off soup and add vinegar.  Salt and pepper to taste.  Ladle soup into small oven-safe bowls or ramekins and top with a couple pieces of toasted bread.  Cover generously with a mixture of the two cheeses (there aren’t amounts or ratios- it’s okay to eyeball!) Sprinkle with a little extra thyme and then place in middle rack in oven with the broiler on to melt cheese.  Be careful, those bowls are hot!