1tspbalsamic vinegar-plus more for garnish, if desired
6slicessour dough bread-or your fav
Set oven to 425F. In a large dutch oven (the one you will be using to make the soup), place beef bones and season with 1/4 teaspoon each of salt and pepper. Bake for 25 minutes. Remove from oven, let cool. Then remove bone marrow from bones. Place marrow in small food processor and pulse until smooth. Lay to one side for later use.
In a saucepan, add beef stock and star anise. Turn on low and heat up for use later.
Using the same dutch oven that you cooked the beef bones, heat tbsp. of olive oil with 1 tsp of butter on low medium low. Add onions and season with 1/2 tsp each of salt and pepper. Cook (don't brown) for 10 minutes. After 10 minutes, add 1/2 cup of hot water. Repeat this process two more times, so that the onions have cooked about 30 minutes in total. Then, add 3 tsp (1 tbsp.) of thyme and garlic and cook for another 5 minutes.
Turn up heat slightly and deglaze with brandy. Cook for about 3 minutes.
From a height, gently add 2 tbsp. of flour and stir through the onions until absorbed, about a minute or so.
Add beef stock (remove star anise), worcestershire sauce, balsamic vinegar , 1 tsp thyme, 1/2 tsp pepper and 1 tsp salt. Bring to a low simmer and cook for 5 minutes.
Remove about 3 cups of the mixture from the dutch oven. Using an immersion blender, blitz that 3 cups until smooth and then add back to the remaining mixture in the dutch oven. Stir to combine.
Divide mixture among oven safe bowls. Using your reserved bone marrow, spread some on each bread slice. Place bread (bone marrow side up) on top of soup and then top with 2 tbsp. of cheese.
Place bowls on a sheet pan (helps with any spillage) and broil on high for about 2 minutes. Remove and garnish with thyme and drizzle of balsamic vinegar (if desired).