Set the oven to 400 F.

There are two ways to make this quiche. If you have a cast-iron or other oven-proof skillet, you can make the quiche right in the skillet. This cuts down on dishes. Otherwise, start with a regular skillet and later transfer everything to a pie plate to bake.

Melt the butter in a skillet over medium heat. Add your onion slices and sprinkle a bit of salt and pepper over them. Cook the onions until they are golden brown and starting to caramelize. If your pan is oven-proof, simply remove it from the heat and spread the onions evenly across the bottom. Otherwise, butter a pie plate and scoop the onions into it, creating an even layer on the bottom. The onions add a crust-like texture and a bit of crunch.

A note on vegetables: For things like broccoli, cauliflower or winter squash, I suggest steaming or cooking them before adding them to the quiche to ensure they'll be fully cooked. For tomatoes, zucchini, spinach or any other quick-cooking vegetable, just use them fresh.

Spread the vegetables evenly over top of the onions. The dish or pan should look fairly full.

In a bowl, use a fork to lightly beat the eggs with the milk, cheese, salt, and pepper, just enough to break up the yolks and whites. This is a savory custard mixture. Pour the custard over the vegetables and onions and enjoy watching it fill in all the free spaces.

Bake the quiche in the oven for 1 hour. Once the surface is lightly brown all the way across, it's fully cooked.

Let the quiche cool for about 20 minutes, then slice into wedges and serve with a side salad.