Ingredients
4 Tbsp. unsalted butter
3 large yellow onions, thinly sliced into half-moons
2 Tbsp. all-purpose flour
Kosher salt
1/2 cup dry white wine
4 cups low-sodium beef stock
2 cups low-sodium chicken stock
8 sprigs thyme, plus more for serving
Freshly ground black pepper
8 baguette slices
1 cup finely shredded Gruyère
How to:
In a large pot over medium heat, melt butter. Add onions and cook, stirring occasionally, until deeply golden brown, 45 to 60 minutes.
Add flour and cook, stirring, until incorporated, 1 to 2 minutes; season with salt. Add wine, bring to a simmer, and cook, stirring occasionally, until evaporated, 1 to 2 minutes. Add beef stock, chicken stock, and thyme and bring to a boil. Reduce heat to medium-low and bring to a simmer. Cook, stirring occasionally, until liquid is slightly reduced and flavors have melded, about 15 minutes. Remove thyme; season with salt and pepper.
Heat broiler to high. Ladle soups into heatproof ramekins. Top each with 2 bread slices, then top with cheese. Broil soup, watching closely, until bubbling and golden, 1 to 2 minutes.
Top soup with more thyme.