Caramelized Onion and Radicchio Quiche

1 pie crust, unbaked, homemade or store bought
1 egg white
3 tablespoons Gruyere cheese, or Swiss, grated
3 tablespoons extra-virgin olive oil
1 red onion, halved and thinly sliced
1 1/4 teaspoons kosher salt
1/4 teaspoon sugar
8 ounces radicchio, halved and thinly sliced
1 teaspoon balsamic vinegar
4 large eggs
1 cup heavy cream
1/4 teaspoon nutmeg
1/2 teaspoon black pepper
1 tablespoon unsalted butter, cubed
 

Preheat the oven to 375 degrees. Press pie crust (homemade or store bought) into a 9-inch pie pan. Line the dough with foil or parchment paper and fill with pie weights, rice or dried beans. Bakes for 20 minutes and then remove the pie weights and foil and bake for an additional 5-7 minutes or until crust is lightly golden. Take the crust out of the oven and sprinkle two-thirds of the gruyere or swiss cheese on the bottom in an even layer. return the crust to the oven and bake for an additional 10-13 minutes.

Meanwhile, in a large pan, heat 2 tablespoons of oil over medium heat. Add the onion, 1/2 teaspoon of salt and sugar and cook, stirring occasionally, until the onion is soft and browned, about 15 minutes. Stir in the radicchio and the remaining tablespoon of olive oil and 1/4 teaspoon salt and cook, stirring constantly, until the radicchio is very wilted and the mixture forms a jam-like consistency, about 10 minutes Stir in the balsamic vinegar and cook for 1 more minute.

In a medium bowl, whisk together eggs, cream, nutmeg and the remaining 3/4 salt and pepper. When the crust is lightly browned and the cheese is melted, sprinkle on half of the onion-radicchio mixture and carefully pour in the egg mixture. Dot the top with pieces of butter and return to the oven to bake for 25-35 minutes, until the top of the quiche is puffed up and golden and the middle is set.

Allow the quiche to cool slightly, about 10 minutes. Serve  topped with the remaining onion-radicchio mixture.