Melt a tablespoon of butter in a skillet or pan over medium heat. Add the onion, a pinch of salt, and sauté until it just begins to caramelize (6-8 minutes). Remove from heat and set aside to cool.
Add the ground meat, crushed pork rinds (or almond flour), Parmesan, heavy cream, parsley, cooked onion, egg, salt, and pepper to a large bowl. Mix everything thoroughly together using your hands and taste for seasoning by cooking a small amount (only way around it!). Form into rounds (either 20 small-ish ones or 14 large).
Heat up a touch of olive oil in your skillet over medium heat and cook the meatballs until brown all over and cooked through. You’ll want to turn them around a few times so they cook evenly. If you’ve got an instant thermometer, your meatballs are cooked through once they reach 165°F/75°C in the center.
Place the cooked meatballs on paper towels to drain. Heat up the marinara sauce, add back the meatballs and mix gently before serving.