Step 1: Preheat your oven to 375°F (190°C). Prepare your pie crust by gently pressing it into a 9-inch pie dish. Crimp the edges decoratively. Line the crust with parchment paper and fill it with pie weights, dried beans, or rice. This crucial step, known as blind baking, helps prevent a soggy bottom crust.
Step 2: Blind bake the crust for 15-20 minutes, or until the edges are lightly golden. Carefully remove the parchment paper and weights. If the bottom seems wet, bake for another 5 minutes uncovered. Remove from oven and set aside to cool slightly. Reduce oven temperature to 350°F (175°C).
Step 3: While the crust is baking, prepare your fillings. In a medium skillet, heat 1 tablespoon of olive oil or butter over medium heat. Add the diced onion and cook until softened and translucent, about 5-7 minutes. Add the bell pepper and cook for another 3-5 minutes until tender-crisp. If using spinach, add it last and cook until wilted, squeezing out any excess moisture. Remove from heat.
Step 4: Evenly sprinkle the cooked vegetable mixture over the bottom of the blind-baked pie crust. Then, sprinkle the shredded cheese over the vegetables.
Step 5: In a large bowl, whisk together the eggs, milk, heavy cream (or half-and-half), salt, black pepper, and a pinch of nutmeg. Whisk until just combined and frothy; avoid over-whisking, which can introduce too much air and lead to a cracked top.
Step 6: Carefully pour the egg mixture over the fillings in the pie crust. Make sure the fillings are submerged. Give the pie dish a gentle shake to ensure the custard settles evenly. Don't overfill; leave a small gap from the top edge of the crust to prevent spillage.
Step 7: Carefully transfer the pie dish to the preheated oven. Bake for 45-55 minutes, or until the center is just set. To check for doneness, gently shake the pie dish; the center should have a slight jiggle, but not be watery. An inserted knife near the center should come out clean. If the crust starts to brown too quickly, you can loosely cover the edges with foil.
Step 8: Once baked, remove the quiche from the oven and let it cool on a wire rack for at least 10-15 minutes before slicing and serving. This resting period is crucial as it allows the custard to fully set, preventing it from collapsing when cut. Enjoy your perfect quiche!