From America's Test Kitchen Season 6: Eggs for Brunch
A really good quiche should have a smooth, creamy custard in a tender pastry crust. The custard should be rich, but not overwhelmingly so, and moist, not dried out. We aimed to find a way to make this perfect pie.
We experimented with multiple combinations of egg and dairy to find the one that would provide just the right balance of richness and lightness. Eggs alone were not rich enough; whole eggs plus yolks provided the degree of richness we wanted. For the dairy component, we found that equal parts of milk and heavy cream worked best. This custard was creamy and smooth. After layering bacon and Gruyère over the bottom of the pie shell—for a classic quiche Lorraine—we poured the custard on top and baked the quiche until it was puffed and set around the edges but still jiggled in the center; the residual heat finished cooking the center without turning the top into a rubbery skin. Before serving the quiche, we let it cool on a wire rack, which is a small but important step; this allows air to circulate under the crust and prevents it from becoming soggy.
The center of the quiche will be surprisingly soft when it comes out of the oven, but the filling will continue to set (and sink somewhat) as it cools. If the pie shell has been previously baked and cooled, place it in the preheating oven for about five minutes to warm it, taking care that it does not burn. Because ingredients in the variations that follow are bulkier, the amount of custard mixture has been reduced to prevent overflowing the crust.