Preheat your oven to 375°F (190°C). This ensures a perfectly cooked quiche with a golden-brown crust.
Prepare the Vegetables: In a pan, heat the olive oil over medium heat. Sauté the onions until translucent, then add the rest of the chopped vegetables. Cook until they're just tender. This step brings out their natural sweetness and ensures they are perfectly cooked within the quiche.
Whisk it up: In a large bowl, combine eggs, heavy cream, milk, salt, pepper, and nutmeg (if using). Whisk until the mixture is smooth. This is the custard base that makes the quiche so irresistibly creamy.
Layering: Spread the sautéed vegetables evenly on the bottom of the pie crust. Sprinkle the shredded cheese over the vegetables. Pour the egg mixture over the cheese. The cheese layer beneath the custard adds a delightful surprise of texture and flavor.
Bake: Place the quiche in the preheated oven and bake for 35-45 minutes, or until the custard is set and the top is lightly golden. To test for doneness, insert a knife in the center – it should come out clean.
Cool & Serve: Let the quiche cool for at least 10 minutes before slicing. This rest period helps the quiche set, making it easier to cut and serve.