Begin by thinly slicing the onions and heating 2 tablespoons of butter in a skillet over medium-low heat. Add the onions and cook, stirring occasionally, for about 20-25 minutes until they are golden brown and soft. Set aside to cool.

In a large mixing bowl, combine 2 pounds of ground beef with half of the cooled caramelized onions. Add 1 teaspoon each of garlic powder and onion powder, followed by 1 teaspoon of dried thyme and 2 tablespoons of Worcestershire sauce. Crack in 1 egg and sprinkle in breadcrumbs. Mix gently.

Transfer the meat mixture into a greased loaf pan and shape it into a neat loaf. Preheat the oven to 350°F (175°C) and bake for 45-50 minutes until the internal temperature reaches 160°F (71°C).

Spread the remaining caramelized onions evenly over the top, then layer slices of Swiss cheese on top. Bake for an additional 10-15 minutes until the cheese has melted and is bubbly.

Let the meatloaf rest for about 5 minutes before slicing. Serve with your favorite sides.