Description
A deeply savory, soul-warming French onion soup with a rich beef broth base, piled with jammy caramelized sweet onions and finished with crusty toasted baguette slices under a blanket of melted Gruyère and Parmesan cheese. The broth is intensely beefy with layers of caramelized sweetness balanced by fresh thyme and a splash of balsamic vinegar for brightness.
Ingredients
- 3 tbsp unsalted butter
- 2 tbsp olive oil
- 4 large yellow onions (about 3 lb), halved through the root and thinly sliced into half-moons
- 1 tsp kosher salt, divided
- 1/2 tsp freshly ground black pepper, divided
- 1 tsp granulated sugar
- 2 tbsp all-purpose flour
- 6 cups low-sodium beef broth (48 fl oz)
- 2 cups water (16 fl oz)
- 3 sprigs fresh thyme, plus 1 tsp fresh thyme leaves for garnish
- 1 bay leaf
- 1 tbsp balsamic vinegar
- 8 slices French baguette, cut 1/2-inch thick on a slight diagonal
- 2 tbsp extra-virgin olive oil, for brushing baguette
- 1 garlic clove, peeled and halved
- 8 oz Gruyère cheese, coarsely grated (about 2 cups)
- 2 oz Parmesan cheese, finely grated (about 1/2 cup)
Instructions
- In a 5- to 6-quart heavy-bottomed Dutch oven or enameled cast-iron pot, melt the butter with the 2 tablespoons of olive oil over medium heat until the butter foams and the foam just begins to subside, about 2 minutes. Add all of the sliced onions and 1/2 teaspoon of the kosher salt, and toss to coat evenly with the fat using a wooden spoon.
- Cook the onions over medium heat, stirring every 3 to 4 minutes, until they soften, release their liquid, and reduce in volume by about half, approximately 12 to 15 minutes. The onions should look glossy and translucent but not yet browned.
- Reduce the heat to medium-low and continue cooking the onions, stirring every 5 to 6 minutes and scraping the bottom of the pot to release any browned bits, until they turn a deep golden amber color and taste sweet and jammy, about 35 to 40 minutes more. If the onions begin to scorch or stick aggressively, add 2 tablespoons of water and scrape up the fond, then continue cooking.
- Stir in the granulated sugar and the remaining 1/2 teaspoon of kosher salt and 1/4 teaspoon of black pepper, and cook for 2 minutes more over medium-low heat to encourage final caramelization. The onions should be mahogany brown, deeply fragrant, and reduced to roughly 2 cups in volume.
- Sprinkle the all-purpose flour evenly over the caramelized onions and stir constantly for 2 minutes to cook out the raw flour taste and create a light roux that will thicken the broth slightly. The mixture will look pasty and slightly dry.
- Pour in 1 cup of the beef broth and scrape the bottom of the pot thoroughly with a wooden spoon to dissolve all the browned fond; this is where the deep savory flavor lives. Once the bottom is clean, add the remaining 5 cups of beef broth, the 2 cups of water, the thyme sprigs, bay leaf, and the remaining 1/4 teaspoon of black pepper.
- Increase the heat to medium-high and bring the soup to a gentle boil. As soon as bubbles break the surface around the edges, reduce the heat to low and simmer, partially covered with the lid slightly ajar, for 20 minutes. Skim any foam that rises to the surface with a spoon and discard.
- Remove the pot from the heat, discard the thyme sprigs and bay leaf, and stir in the balsamic vinegar. Taste and adjust seasoning with additional kosher salt and black pepper as needed; the broth should be rich, savory, and rounded with a whisper of sweetness and acid.
- While the soup simmers, preheat the oven to 400°F / 204°C and arrange a rack in the upper third of the oven. Arrange the baguette slices on a rimmed baking sheet, brush both sides lightly with the 2 tablespoons of extra-virgin olive oil, and toast until golden and crisp at the edges but still slightly tender in the center, about 8 to 10 minutes, flipping once halfway through. Rub one side of each toasted slice with the cut garlic clove while still warm.
- Ladle the hot soup into 4 oven-safe French onion soup crocks or 12-ounce ramekins placed on a sturdy rimmed baking sheet. Fill each crock to within 1/2 inch of the rim to leave room for the bread and cheese without overflowing.
- Place 2 toasted baguette slices on top of the soup in each crock, covering the surface as much as possible without submerging the bread completely. The bread should float on the soup and form a raft that will hold the cheese layer.
- Sprinkle each crock generously with the grated Gruyère, about 1/2 cup per serving, making sure the cheese extends slightly over the rim of the crock so it melts down the sides. Follow with 2 tablespoons of grated Parmesan per crock, sprinkling evenly over the Gruyère.
- Carefully transfer the baking sheet with the filled crocks to the oven and broil on high until the cheese is completely melted, bubbling, and deeply browned in spots, about 3 to 5 minutes. Watch closely after 2 minutes to prevent burning, rotating the sheet once for even browning.
- Remove from the oven and let stand for 2 to 3 minutes before serving; the soup will be extremely hot. Garnish each crock with a pinch of fresh thyme leaves and serve immediately with additional black pepper at the table.
Notes
Storage: Cool the soup base completely (without the bread and cheese topping), transfer to an airtight container, and refrigerate for up to 4 days. Freeze the cooled soup base without the bread and cheese in freezer-safe containers for up to 3 months; thaw overnight in the refrigerator before reheating. Reheating: Warm the soup base in a saucepan over medium heat until simmering, then proceed with the toasted baguette and cheese steps above. For quicker weeknight service, broil baguette slices with cheese on top for 2 to 3 minutes until melted, then float them on reheated soup. Crocks retain heat intensely; serve on plates and warn diners the bowls are hot. For deeper flavor, store the soup base overnight in the fridge before reheating.
Nutrition
- Calories: 615
- Sugar: 12g
- Sodium: 1480mg
- Unsaturated Fat: 16g
- Carbohydrates: 58g
- Fiber: 4g
- Protein: 28g
- Cholesterol: 75mg
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