Preheat oven to 425°F and line a 9-inch pie plate with a store-bought pie crust and crimp the edges. A frozen crust works fine too.
See the notes section on broccoli.
Melt the butter in a large skillet over medium-low heat. Add the minced onion and cook, stirring occasionally, until soft; about 2 minutes. Add the broccoli, minced garlic, and 1/4 teaspoon of the salt. (See notes on using fresh or frozen broccoli). Increase the heat to medium and cook until the broccoli is fork-tender and any liquid has evaporated. Set aside.
In a medium bowl, whisk together the milk, eggs, 3/4 teaspoon salt, pepper, nutmeg and cayenne. Set aside.
In the bottom of the crust, add the cooked onion, garlic, and broccoli mixture (save a few broccoli florets to garnish the top of the quiche if you would like). Add the halved cherry tomatoes and sprinkle the shredded cheese and parmesan cheese over the top. Pour in the egg mixture and garnish with a few florets and tomatoes.
Bake 15 minutes in the oven at 425 degrees. Without opening the oven, reduce the temperature to 325° and continue to bake for another 20 to 25 minutes, or until the custard is set and the top is golden brown. Let cool for 10 minutes before cutting into wedges.
Notes
Broccoli:
I have used both fresh broccoli and frozen broccoli in this recipe. If using fresh broccoli, add a bit of water, about 1/3 cup, to the skillet so the broccoli can cook for a couple of minutes.
If using frozen broccoli, do not add water, simply saute with the garlic for about a minute.
Be sure the florets (whether fresh or frozen) are in small florets.
Making Ahead:
Once the quiche is baked, cool completely, cover, and refrigerate. To reheat, cover the quiche with foil and bake at 325F (until just heated).