1- Combine flour, cubed butter, salt, and baking powder in a bowl.

2- Use a pastry cutter or fork to cut the butter into the flour until the mixture resembles coarse crumbs.

3- Add ice cold water and mix until a dough just forms.

4- Wrap the dough tightly in plastic wrap and refrigerate for at least 2 hours.

5- Preheat oven to 375°F (190°C).

6- Roll out the chilled dough on a floured surface to fit a standard pie plate.

7- Gently press the dough into the plate.

8- Prick the bottom and sides thoroughly with a fork.

9- Bake the crust for 10 minutes (par-bake).

10- Remove from the oven.

11- Place the sliced potatoes in a pot of salted boiling water. Cook for 5 minutes, then drain well.

12- In a large bowl, whisk together the eggs, half and half, heavy cream, Swiss cheese, chopped green onions, cooked bacon, ½ teaspoon salt, ¼ teaspoon pepper, and ⅛ teaspoon nutmeg until combined.

13- Stir in the drained boiled potatoes.

14- Pour the filling mixture into the par-baked crust.

15- Reserve 1 tablespoon of the wet egg mixture.

16- Brush the reserved liquid onto the edges of the crust.

17- Bake for 30 to 40 minutes, or until the center is set.

18- If the crust edges begin to brown too quickly (usually after 15-20 minutes), cover them loosely with aluminum foil.

19- Remove the quiche from the oven and let it cool completely before serving.