kosher salt and freshly ground black pepper, to taste
6 thick slices toasted French bread
1 cup shredded Gruyere cheese
Instructions
Place a Dutch oven or large saucepan over medium heat. Heat the vegetable oil and butter until the butter has melted. Add the onions and cook until soft and caramelized, stirring frequently. This will take about 15 to 20 minutes. Turn the heat down and add a splash of water if the onions begin scorching or sticking to the pan.
Add the cornstarch and stir until well blended. Gradually add the beef stock. Taste and add salt and pepper, as needed. Bring to a boil. Reduce the heat to low and simmer, uncovered, for about 20 to 30 minutes.
Preheat the broiler.
Ladle the soup into oven-safe bowls. Place a slice of toasted French bread on each serving and top with a generous amount of shredded cheese.
Place the bowls on a baking sheet and broil just until the cheese is melted and bubbly.