Prepare the Onions:

Heat a skillet over medium heat and cook sliced onions in a tablespoon of butter until golden and caramelized. Set aside to cool slightly.

Mix the Meatloaf:

In a large bowl, combine the ground beef, French onion soup mix, breadcrumbs, eggs, and milk. Mix until just combined.

Add the Layers:

Divide the meat mixture in half.

Press half into the loaf pan to form the base layer.

Sprinkle the caramelized onions and shredded cheese evenly over the layer.

Cover with the remaining meat mixture, sealing the edges to encase the filling.

Glaze and Bake:

Spread ketchup or BBQ sauce over the top if desired.

Bake in a preheated 375°F (190°C) oven for 50–60 minutes or until the internal temperature reaches 160°F (70°C).

Rest and Serve:

Let the meatloaf rest for 5–10 minutes before slicing to retain juices.