Preheat the oven to 350. Combine the shredded potatoes with the oil and season with salt and pepper. Spray a 9 inch round quiche pan (I used Pyrex) heavily with cooking spray and press the filling along the bottom and up the sides until its covered. Bake for 15 minutes until the potatoes are just lightly golden. Saute the leek in the butter for about 10 minutes until translucent and cool for a few minutes. In a bowl mix together the cream, eggs, sour cream and ½ cup of the Mozzarella and season to taste with salt and pepper. Add the leeks and mix well. Pour the mixture into the crust and top with remaining Mozzarella. Bake for about 40 minutes until the center is set and the quiche is golden brown.