Preheat oven to 400 degrees F and Grease a 12" cast iron skillet (or a 9x13" baking dish) with non-stick cooking spray.
In a large bowl combine the sliced potatoes, olive oil, salt, pepper and tapioca powder. Toss until potatoes are well combined and evenly coated in the mixture (without any clumps).
Spread half of the potato mixture evenly across the prepared skillet/baking dish then scatter all of the onion slices evenly on top of the potatoes. Sprinkle half of the grated gruyere and half of the thyme on top of the onions. Add the remaining sliced potatoes on top.
In a separate bowl, whisk together the dairy-free creamer, garlic, nutmeg, cayenne and paprika until well-combined.
Evenly pour over the potatoes. Top with remaining cheese and thyme.
Cover tightly with foil then using a knife, carefully cut a 1-inch slice in the center of the foil to allow the steam to vent. Place into oven and cook until potatoes are tender, about 45 minutes.
After 45 minutes, uncover then add back into the oven until cheese is brown and bubbly, about 10 more minutes.
Allow to cool for 5-10 minutes before serving. Garnish with freshly chopped parsley and flakey salt (like Maldon) if desired! Enjoy!