Preparation

1. Heat the oven to 350°F. Lightly oil a 9-inch pie pan.
2. Place the chopped bacon in a large skillet over medium heat. Stir occasionally, until bacon is crisp and brown, about 4 minutes. Transfer to a large bowl, and pour off all but a tablespoon of bacon fat (you can save for another use, or discard.) Add the onions to the pan and cook over medium heat until soft and golden, about 5 minutes. Transfer to the bowl with the bacon. Add the eggs and milk to the bowl and whisk to combine, then stir in all but 1/4 cup of the Swiss cheese, the salt, pepper and scallions. Pour into the prepared pan and top with reserved cheese.
3. Bake for about 45 minutes, until the quiche is puffed and golden. Let cool on a rack for 5 minutes before cutting. Keeps for 4 days, tightly covered, in the refrigerator.