In a large frying pan over medium-low heat, sauté all diced onions in oil until caramelized. Transfer to a medium bowl and set aside to cool.

Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius).

In a mixing bowl, combine mashed sweet potatoes with three eggs, two tablespoons potato starch, and salt and pepper to taste. Add remaining eggs, potato starch, salt, and pepper to caramelized onions and mix to combine. Spray muffin tins with oil spray and divide half of the sweet potato mixture evenly among 14 muffin cups. Spoon onion mixture over the sweet potato mixture, then divide remaining sweet potato mixture over onions, covering completely.

Bake for 25–30 minutes, or until set.