Preheat the oven to 350°F (175°C).

In a skillet, melt the butter over medium heat. Add the sliced onions and cook until they are caramelized, which should take about 15-20 minutes.

In a large bowl, combine the ground beef with the caramelized onions. Season with salt and pepper to taste.

Shape the mixture into a loaf and place it in a baking dish.

Pour the beef broth over the meatloaf.

Bake in the preheated oven for about 1 hour, or until the internal temperature reaches 160°F (70°C).

Let it rest for 10 minutes before slicing and serving.