Put raw sliced onions in casserole. 3 ingredients later: Comfort food you didn’t know you needed

Preheat: Preheat your oven to 375°F (190°C).
Caramelize Onions: In a large skillet over medium heat, cook the sliced onions until they are soft and caramelized, about 20-25 minutes. Stir occasionally to prevent burning.
Assemble: Transfer the caramelized onions to a baking dish and spread them evenly. Pour the beef broth over the onions, ensuring they are well-coated. Sprinkle the shredded Gruyère cheese evenly over the onions. Top with breadcrumbs, spreading them out to cover the cheese layer.
Bake: Bake in the preheated oven for 20-25 minutes, or until the cheese is bubbly and the breadcrumbs are golden brown.
Cool: Allow to cool slightly before serving.