Preheat your oven to 375°F (190°C) and grease a 16-ounce ramekin or small baking dish with the ghee.
In a small skillet over medium heat, sauté the fresh spinach until completely wilted, then squeeze out any excess moisture and roughly chop.
Separate the yolks from the 3 large eggs, placing the yolks in one bowl and the whites in a large, clean mixing bowl.
Add the liquid egg whites and the cream of tartar to the bowl with the fresh egg whites.
Using a hand mixer or stand mixer, beat the egg whites on high speed until stiff peaks form.
In the bowl with the egg yolks, whisk in the non-fat Greek yogurt, shredded sharp cheddar cheese, wilted spinach, sea salt, and black pepper until well combined.
Gently fold one-third of the whipped egg whites into the yolk mixture to lighten it, then very carefully fold in the remaining whites until just combined, being careful not to deflate the air.
Pour the mixture into the prepared ramekin and bake for 20-25 minutes until the soufflé has risen and the top is golden brown.
Serve immediately while the soufflé is at its peak height.