Secret #1: The right ratio of eggs to dairy.
The eggs need to be diluted with milk or cream but if you use too much dairy, there will not be enough proteins form the eggs to set the quiche. The right ratio is 1/2 cup dairy for each large egg. A four-egg quiche should have 2 cups of milk or cream or half and half.
Secret #2: Baking the quiche until it is just right.
As stated, a quiche relies on the coagulation of the egg proteins to set into a firm pie filling. A mixture of egg whites and egg yolks coagulates at 165 degrees. These same proteins become tough at 185 degrees. So your target temperature is 170 degrees.
The secret of a well-baked quiche is a thermometer. To test for doneness, insert a thermometer right in the center of the quiche half way through the filling. When the temperature reaches 170 degrees, remove the quiche from the oven. If you let it cook longer than that, the temperature of the filling toward the edges where the filling sets first, may be over 185 degrees.
Secret #3: Avoiding a burnt crust.
By the time the center of the quiche reaches 170 degrees, the crust may be over cooked, even burnt.
The secret of avoiding a burnt crust is to protect the crust. A dark pie pan absorbs heat and while they are preferable for avoiding soggy crusts with fruit pies, they are not desirable for quiches. A light pan, especially a stainless steel pan, reflects heat. (By the way aluminum is a much better conductor of heat than is steel; never use an aluminum pan for quiche.)
A pie crust shield or aluminum folded around the edges of the pie is usually necessary to protect the protruding edges of the crust. Both reflect heat. A pie crust shield is easier to use than aluminum foil which always seems to fall off or protrude into the filling.
Secret #4: Adding the right amount of cheese.
Cheese performs two functions in our quiche: It delivers flavor and adds fat that contributes to a pleasing “mouth feel” and substance. We prefer a cup of grated cheese in a four egg quiche but admittedly, the amount of cheese is a matter of taste. For us, less than a cup of cheese and the quiche tastes light and with insufficient substance. If you use cream with its high fat content, you can use less cheese.
All else is matter of taste and preference: what meats and vegetables you add, what seasonings, and what cheese that you add.