Not pre-baking the vegetables for the filling

Making quiche is not a quick process, but it is critical not to skip any steps in order to save time. Imagine spending hours preparing the perfect-looking quiche only to bite into it and discover that the vegetables are still crunchy. This is most likely due to the use of raw vegetables in the filling. Because most vegetables take longer to cook than custard, you should prepare the vegetables for your quiche filling ahead of time. This is the best way to ensure an evenly baked pastry. Onions, mushrooms, and spinach are best sautéed, whereas broccoli is best roasted or steamed. This not only prevents overly crunchy bites but also helps release moisture from the vegetables, which can ruin your filling.

Similarly, it is best to pre-cook meats for your quiche. Bacon and sausage are high in fat, and you don't want a pool of grease to form in your quiche. Cooking the meats ahead of time allows for better flavor development through browning and renders out the fat, giving you control over the grease level.