Grease a large heavy-based saucepan or Dutch oven with ghee.
Add the onion and cook over medium-high heat for 5 to 8 minutes, until lightly browned.
Set aside to cool slightly.
Preheat the oven to 350°F / 175°C.
In a large bowl, combine the ground beef, salt, tomato paste, Dijon mustard, caraway seeds, egg, sauerkraut, coconut flour, and the cooked onion.
Mix until just combined.
Place the meat mixture on a large piece of heavy-duty baking foil and flatten it into a large rectangle. Lay half of the pastrami slices over the meat in a single layer, followed by half of the grated cheese.
Starting from a short side, carefully roll up the meatloaf, using the foil to help lift and guide it.
Peel the foil away as you roll, finishing with the seam side down.
Transfer the meatloaf (still on the foil) to a baking dish.
Bake uncovered for 30 minutes.
While the meatloaf bakes, prepare the Russian dressing by mixing all of its in a small bowl.
Set aside.
After 30 minutes, remove the meatloaf from the oven. Increase the oven temperature to 400°F / 200°C. Lay the remaining pastrami slices over the top and sprinkle with the remaining cheese. Return to the oven and bake for another 10 minutes, or until the cheese is melted and an instant-read thermometer registers 160°F / 71°C.
Let the meatloaf rest for 5 to 10 minutes before slicing.
Serve warm, drizzled with the Russian dressing and roasted Brussels sprouts on the side.
Squeeze the sauerkraut thoroughly to remove excess moisture. This prevents the meatloaf from becoming watery and helps it hold its shape.