In a medium bowl whisk together flour, sugar, and salt. Add cold cubed butter and using a pastry cutter or your fingertips, cut butter into flour until mixture resembles coarse crumbs with some pea-sized pieces remaining.

Sprinkle cold water over the mixture 1 tablespoon at a time, tossing with a fork until dough just comes together. Do not overwork. Gather into a disk, wrap in plastic, and chill in the refrigerator for at least 30 minutes.

Preheat oven to 375°F (190°C). On a lightly floured surface roll chilled dough to a 12-inch circle about 1/8-inch thick and transfer to a 9-inch deep-dish tart or pie pan. Trim and crimp edges. Line crust with parchment and fill with pie weights or dried beans. Blind-bake for 15 minutes, remove weights and parchment, then bake 5–7 more minutes until the crust is set and lightly golden. Reduce oven to 350°F (175°C). Let crust cool slightly.

Filling

Cook the bacon in a skillet over medium heat until crisp. Transfer to a paper towel-lined plate to drain then chop into small bits. Reserve about 1 tablespoon bacon drippings for additional flavor (optional).

In a large bowl whisk together the eggs, whole milk, heavy cream, reserved bacon drippings (if using), salt, pepper, and nutmeg until smooth and slightly frothy.

Scatter shredded Swiss cheese evenly in the prebaked crust. Evenly distribute chopped bacon and sliced green onions over the cheese.

Pour the egg-cream mixture slowly into the crust over the fillings, filling to about 1/4 inch from the rim. Gently tap the pan on the counter to release air bubbles and settle the custard.

Bake at 350°F (175°C) for 35–45 minutes, or until the center is set but still slightly jiggly and the top is lightly golden. If the crust edge browns too quickly, cover with foil. Remove from oven and let rest 10–15 minutes before slicing.

Hollandaise

While the quiche bakes or rests, prepare the hollandaise using a double boiler or a heatproof bowl set over barely simmering water (make sure bowl doesn't touch the water). Whisk egg yolks and lemon juice vigorously until mixture thickens and doubles in volume, about 2–3 minutes.

Slowly drizzle the warm melted butter into the yolk mixture while whisking constantly to emulsify. Continue until sauce thickens to a pourable consistency. Remove from heat and whisk in cayenne and salt. If sauce gets too thick, whisk in a teaspoon or two of warm water to loosen.

Keep hollandaise warm (but not hot) until serving. Taste and adjust salt or lemon as needed.

Sides / Garnish

Prepare baked peaches while the quiche bakes: Preheat oven to 375°F (if not already). Place peach halves cut-side up in a small baking dish. Dot each half with a little butter, sprinkle with brown sugar and cinnamon. Bake 12–15 minutes until peaches are tender and glazed. Remove and keep warm.

To serve: slice quiche into wedges. Drizzle a spoonful of hollandaise over each wedge, then sprinkle with extra bacon bits and sliced green onions. Plate with a baked peach half and a muffin or strudel on the side.

Leftovers: refrigerate covered for up to 3 days. Reheat gently in a 325°F oven until warm to preserve texture; rewarm hollandaise gently over a double boiler or whisk in a little warm water if it separates.