Preheat your oven to 350 degrees f. and line a 9x5-inch loaf pan with parchment paper.
Heat the ghee, tallow, or oil in a large skillet over medium heat.
Sautee your thinly sliced onions, stirring quite often, for 25-30 minutes, until caramelized and golden brown. Remove from the heat and allow to cool for a bit.
In a large bowl, add the beef, beaten eggs, almond flour, mustard, thyme, garlic, Worcestershire sauce, sea salt, and pepper. Add in about 2/3 of the caramelized onions, reserving 1/3 for topping later.
Stir well to combine. Transfer to your prepared loaf pan and press gently to fill in all of the corners and make it nicely shaped as a loaf.
Bake for 50-60 minutes or until the center temperature reaches around 150 degrees f.
Remove from the oven and sprinkle with your freshly shredded cheese while it's hot.
Top with the remaining caramelized onions as shown.
If desired, you can place your meatloaf under the broiler oven for a few minutes to brown the onion and cheese toppings.
Slice and serve hot