Potatoes: Preheat oven to 350 °F/ 177 °C. Grease well a 9-inch cast iron or pie pan with melted ghee. Slice the potato into very thin rounds (or use a mandoline) to about ⅛-inch thickness. Lay the potato rounds from the edge of the wall to the bottom of the cast iron. Try to overlap each potato rounds so they touch each other. Slightly crisp up the potato rounds over stovetop for about 5 minutes over medium to medium-low heat. Be careful not to burn the potato slices.
Onions: Sauteed thin sliced onions over a skillet. Season with a little bit salt until the onions turn softer and slightly caramelized but not burnt. Set aside.
Egg mixture: In a large bowl combine the eggs, scallions, coconut milk, and sprinkle of sea salt and black pepper. Gently whisk well.
Bake: Add prosciutto slices over potato rounds and spread out sauted onions evenly over prosciutto. Pour in the egg mixture. Bake for about 30-35 minutes or until the frittata is not jiggle in the center when moved. *Oven temperature varies, check after 25 mins.
Salsa: In the meantime, prepare salsa and set aside in the fridge.
Serve: Let frittata cool slightly before using a spatula to loosen edges of frittata from skillet.* Cut frittata in wedges and top with mango salsa. Serve in room temperature.
The potato rounds will firm/crisp up a bit more after they have come to room temperature.
In my experiment, I found it easier to loosen the edges and bottom of frittata and cut into wedges this way.
If you use a larger size skillet (larger than 9-inch), you'll need more potato rounds to cover the skillet and please also increase the egg batter quantity (I.e. eggs, scallions, prosciutto, coconut milk etc.) The egg batter should cover up to a little less than three quarter of the edge wall of the potato rounds in the skillet.
To make ahead or save extra leftover, store the frittata in the fridge (separate from the mango salsa) with a glass and airtight container for up to 3 days for maximum freshness and flavor.