Heat the oven to 375°F. Fit the pie crust into a 9-inch pie plate, prick the bottom with a fork, cover it with parchment, and add pie weights or dried beans.

Blind-bake the crust for 10 minutes. Remove the parchment and weights, then bake for another 3–5 minutes, until the surface looks dry but is not browned.

Heat the oil or butter in a skillet over medium heat. Cook the onion for 3–4 minutes until softened, add the garlic, and cook for about 30 seconds.

Add the fresh spinach and cook just until wilted. If using frozen spinach, thaw it and squeeze it very dry before adding it. Stir in the chopped artichokes and cook for 1–2 minutes, then remove the skillet from the heat.

Whisk the eggs, half-and-half, salt, pepper, and optional red pepper flakes together. If using cream cheese, whisk or blend it into the custard until mostly smooth.

Spread the spinach-artichoke mixture over the partially baked crust. Sprinkle the mozzarella and Parmesan over the vegetables, then pour the egg mixture over everything.

Bake at 375°F for 35–45 minutes, until the edges are set and the center has a slight, gentle wobble. Cool the quiche for 10–15 minutes before slicing so the custard can finish setting.