Heat 1 to 2 tablespoons olive oil in a skillet over medium heat. Add the thinly sliced onions and a pinch of salt. Cook gently, stirring occasionally, until the onions are deeply golden and sweet, about 20 to 25 minutes. Remove from heat and let cool slightly.

In a large bowl, add the ground meat, breadcrumbs (or almond flour), shredded Swiss or Gruyère, the egg, garlic powder, dried thyme, a good pinch of salt, and several grinds of black pepper. If you’re using the onion soup mix, sprinkle it in now.

Fold the cooled caramelized onions into the meat mixture just until combined. Overmixing will make the loaf dense.

Shape the mixture into a loaf using your hands and place it on a baking sheet or into a lightly greased loaf pan. Smooth the top so it cooks evenly.

Preheat the oven to 375°F (190°C). Bake the meatloaf 50 to 60 minutes, or until an instant-read thermometer reads 160°F (71°C) for beef or 165°F (74°C) for turkey in the center. If the top begins to brown too quickly, tent loosely with foil.

Remove the meatloaf from the oven and let it rest 5 to 10 minutes before slicing. Resting locks in juices and makes cleaner slices.