In a large skillet, heat the olive oil over medium heat. Add the sliced onions, sugar, salt, and pepper. Cook, stirring occasionally, until the onions are caramelized and golden brown, about 15-20 minutes.
In a mixing bowl, whisk together the eggs, sour cream, ricotta cheese, thyme, and nutmeg until smooth and well combined.
Once the onions are caramelized, let them cool slightly and then fold them into the egg and cheese mixture.
Preheat your oven to 375°F (190°C).
Place the pre-made pie crust in a pie dish. Pour the onion mixture into the crust, spreading it evenly.
Bake in the preheated oven for 30-35 minutes, or until the filling is set and the top is lightly golden.
Remove the pie from the oven and let it cool for about 10 minutes. Garnish with fresh chopped parsley before slicing.
Notes
Serve warm, sliced into wedges, with a side of extra sour cream or a fresh green salad.