Prepare the Broccoli. Preheat your oven to 375°F. Lightly steam or blanch the broccoli florets just until tender-crisp, then drain well. Excess moisture is the enemy of a good quiche, so let the broccoli cool and dry slightly.
Prep the Crust. Place the pie crust into a 9-inch pie dish or tart pan. Crimp the edges if desired. For best results, lightly pre-bake (blind bake) the crust for 8–10 minutes. This helps prevent a soggy bottom.
Make the Egg Custard. In a large bowl, whisk together the eggs, milk or half & half, salt, pepper, and nutmeg if using. Whisk until fully combined, but don’t overbeat. You don’t want too much air.
Assemble the Quiche. Sprinkle the broccoli and sun-dried tomatoes evenly over the crust. Add onions and cheese, distributing them evenly. Slowly pour the egg mixture over the fillings.
Bake. Bake uncovered for 35–45 minutes, or until the center is just set and no longer jiggly. A knife inserted near the center should come out mostly clean.
Rest and Serve. Let the quiche rest for at least 10–15 minutes before slicing. This allows the custard to set fully and makes cleaner slices.