French Onion Recipe

Prepare onions

Peel the onions and slice them in half from root to tip. Lay each half flat and slice thinly (about 1/8-inch). Aim for even slices so they caramelize uniformly.

Heat fat

In a large heavy-bottomed pot or Dutch oven, melt the butter with the olive oil over medium heat. The oil raises the smoke point of the butter and helps prevent burning.

Caramelize onions

Add the sliced onions, sugar, and kosher salt to the pot. Stir to coat and spread the onions in an even layer. Cook over medium to medium-low heat, stirring every 4–6 minutes, adjusting the heat so the onions brown slowly but do not burn. This process takes 35–45 minutes. Scrape browned bits from the bottom with a wooden spoon as they form.

Season and deglaze

When the onions are deeply golden-brown and jammy, and the pot has browned fond on the bottom, sprinkle the flour over the onions and stir for 1–2 minutes to cook the raw flour taste. Add the white wine (or sherry) to deglaze, scraping up all browned bits. Let the wine reduce by half, about 2–3 minutes.

Simmer soup

Add the beef and chicken broths, Worcestershire sauce, thyme sprigs, and bay leaves. Increase heat to bring to a gentle simmer, then reduce heat to low. Simmer uncovered for 20–30 minutes to allow flavors to meld. Taste and adjust seasoning with additional salt and pepper if needed. Remove thyme sprigs and bay leaves before serving.

Prepare crostini

Preheat the broiler. Brush both sides of the baguette slices lightly with olive oil and arrange on a baking sheet. Toast under the broiler until golden on both sides, about 1–2 minutes per side (watch carefully). Rub the warm toasts with the cut side of the garlic clove for a hint of garlic flavor.

Assemble bowls

Ladle the hot soup into ovenproof bowls or crocks, leaving about 1/2-inch headspace. Place 1–2 toasted baguette slices on top of each bowl (you can break them to fit). Pile a generous handful of grated Gruyère over the bread to cover, and sprinkle a little grated Parmesan if using.

Gratinée

Place the filled bowls on a baking sheet and broil until the cheese is melted, bubbling, and lightly browned, about 2–4 minutes depending on broiler strength. Alternatively, bake at 450°F (230°C) until cheese is melted and golden, about 8–10 minutes. Remove carefully (bowls will be hot). Let cool 2 minutes before serving.

Finish

Garnish with a small thyme leaf if desired and serve immediately. Warn diners that the gratinée bowls will be very hot.