Preheat the oven to 350 degrees Fahrenheit.
Grate the potatoes in a large bowl and sprinkle them with salt and pepper.
Gather all of the potato shreds in a paper towel and squeeze out as much liquid as you can.
Heat a large cast iron skillet over medium heat and add the oil and butter. Once it has melted, start pressing the potatoes in the skillet and up around the sides to form a crust. Make sure the layer is even by using a wooden spoon to continuously press the potatoes down and up the sides. Continue cooking the crust and pressing, until the bottom and edges of the crust brown. This should take about 12 to 15 minutes.
While the crust is cooking, sauté the vegetables you're using and whisk together the eggs, garlic, milk, cheese, salt and pepper. To caramelize the onion, cut it in long strips and sauté it in about 2 tbsp olive oil for 2-5 minutes, stirring frequently.
Fold in the herbs. Pour the egg filling into the crust.
Bake the quiche for 35 to 45 minutes- until golden on top and set in the center. Let the quiche cool before serving and sprinkle with additional cheese and fresh herbs.