Classic French Onion Soup

Quarter 3 yellow onions with skin on and slice 1 head of garlic in half across the center.

Place 1.5 kg beef marrow bones into a large stockpot. Add the quartered yellow onions, halved garlic head, 2 chunked carrots, 3 chunked celery stalks, 3 bay leaves, 8 fresh thyme sprigs, and 4 sage sprigs. Cover completely with 3.5 liters of cold water. Bring to a simmer over medium-high heat, then reduce heat to medium-low and simmer gently for 3 hours, periodically skimming off foam and impurities using a skimmer. Cover with a lid.

Halve 2 Vidalia sweet onions and 2 white onions from top to bottom. Peel off papery skins and trim stem ends. Slice vertically pole-to-pole into uniform medium-thick strips. Trim the ends of 3 shallots, peel off skin, and slice thinly across into rounds.

Melt 30g unsalted butter in a heavy-bottomed Dutch oven over medium-low heat. Add all sliced Vidalia onions, white onions, and shallots. Stir continuously for 15 minutes to coat thoroughly in butter. Season with 1 tsp salt, cover with lid, and cook covered for 15 minutes until onions become completely soft and translucent without browning.

Uncover pot and stir in 1 tbsp brown sugar. Cook uncovered over medium-low heat for 45 to 60 minutes, stirring periodically to allow brown fond to build up on bottom and sides of pot. As fond builds up, pour in a splash (about 60ml) of hot beef stock and scrape up fond using a wooden spoon. Continue stirring and scraping until onions turn dark brown, deeply caramelized, sweet, and jammy.

Pour in 120ml dry white wine. Scrape up all remaining caramelized browned bits off the bottom and inner sides of the pot with a wooden spoon. Simmer uncovered for 3 to 5 minutes until liquid reduces down by about 80%.

Pour the simmered beef stock through a fine-mesh strainer into a large measuring cup to yield 1.2 liters of clear beef stock. Pour stock into Dutch oven over caramelized onions. Add 0.5 tsp cracked black pepper, 2 bay leaves, and 4 fresh thyme sprigs. Stir well, turn heat to very low, cover with lid, and simmer gently for 45 minutes.

Slice 1 day-old French baguette diagonally into 8 even crostini slices (about 1.5 cm thick). Arrange slices in a single layer on a wire rack set in a sheet tray. Slice 1 garlic clove in half and rub cut surface lightly over top of each baguette slice. Bake in preheated oven at 180°C (350°F) for 10 minutes until lightly toasted and dried out.

Trim outer rinds off 150g Gruyere cheese, 150g Comte cheese, and 150g Fontina cheese. Grate all three cheeses vertically downwards along the full length of a box grater to produce long strands. Toss and mix all three grated cheeses together thoroughly by hand to create a uniform cheese blend.

Uncover soup pot and stir in 20g cold unsalted butter vigorously until fully melted and emulsified into soup broth. Fish out and discard cooked thyme sprigs and bay leaves. Taste broth, adjust seasoning with 0.25 tsp cracked black pepper and 0.5 tsp salt as needed. Turn off heat, cover pot, and keep warm.

Arrange 4 oven-safe ceramic soup crocks on a rimmed baking sheet tray. Drizzle 0.5 tbsp dry sherry into bottom of each crock. Ladle hot onion soup into crocks until filled near top (leaving about 1.5 cm space). Float 2 garlic-rubbed toasted baguette slices on top of soup in each crock. Mound generous handfuls of shredded cheese blend over bread and spilling down rim. Top each bowl with 1 fresh sprig of thyme.

Place baking sheet tray with assembled soup crocks into oven set to high broiler (230°C / 450°F). Broil for 3 to 5 minutes while watching closely through oven window until cheese melts into a bubbling, molten, dark golden-brown crust. Carefully remove baking tray using heavy oven mitts and serve immediately.