For the caramelized onions:
2 large yellow or sweet onions, thinly sliced
2 tablespoons unsalted butter
1/2 cup vegetable or beef stock (we like Kitchen Basics brand for this recipe)
Remaining ingredients:
1 14-ounce store-bought pie crust, rolled to just under 1/4" thickness
1 1/2 cups Gruyère or Swiss cheese, grated
6 large eggs
1/2 cup heavy cream or half-and-half
Salt and pepper, to taste
Freshly chopped parsley, for garnish
Preheat your oven to 350 F.
Carefully place the pie crust over a 9-10" round pie dish; press crust down gently so it fits into the bottom and sides of the pan. Trim off excess crust. Dock the crust all over with a fork. Bake for 8-10 minutes. Remove from oven and set aside.
Make the caramelized onions: Heat a large, heavy skillet to medium and add butter. Once butter is melted, add onions and toss to coat with the butter. Cook, stirring every few minutes, until the onions become softened and take on a golden color. The entire process should take about 20-25 minutes. Turn up heat to medium-high and add stock to deglaze the pan, making sure to scrape up the brown bits from the bottom of the pan with a wooden spoon. Season with salt and cook until the liquid reduces by half, about 5-7 minutes. Remove from heat and set aside.
Whisk together eggs, cream or half-and-half in a bowl. Season with salt and pepper.
To assemble the quiche, add half of the onion mixture in an even layer to bottom of the pre-cooked pie crust. Add half the cheese ad pour half of the egg mixture over the cheese. Repeat this process with the remaining onions, cheese and eggs.
Bake at 350 F for 35-40 minutes or until a toothpick inserted in the middle comes out clean. Remove from oven, garnish with parsley, and let sit for a few minutes before serving.