Bacon, Cheddar, and Caramelized Onion Quiche

Firstly, preheat your oven to a high temperature of 350 degrees Fahrenheit (or 175 degrees Celsius). Next, cook the bacon in a large skillet over medium-high heat, stirring occasionally and flipping it frequently until crispy, which should take around 10 minutes. Remove the cooked bacon from the skillet with a slotted spoon and place it on some paper towels to drain off any excess fat. Allow the bacon to cool down for 10 minutes before crumbling it into small pieces and setting it aside.

Now, take out your pastry dough and roll it out using a lightly floured rolling pin to fit a 9-inch pie plate perfectly. Gently place the rolled-out pastry into the pie plate and use a fork to prick some holes in the bottom of the crust.

Place the pastry-lined pie plate into your preheated oven and bake it in the middle rack for 15 minutes. Remove the crust from the oven and give it a light brushing with some beaten eggs. Return the crust to the oven and bake for another 5 minutes.

In a separate pan, melt some butter over medium heat. Add sliced onions to the pan and cook them until they're softened and translucent, stirring occasionally, which should take about 5 minutes. Reduce the heat to low and continue cooking the onions until they're very tender, dark brown, and almost caramelized - this should take around 40 minutes.

In a separate bowl, whisk together the remaining eggs until well combined. Add some sour cream and softened cream cheese to the bowl, then beat everything together with an electric mixer until it's smooth and well combined. Add some salt and pepper to the mixture, then beat everything together again.

Spread the caramelized onions evenly over the pastry crust using some of the remaining butter. Sprinkle 1/2 cup of Cheddar cheese over the onions, then place the crumbled bacon on top. Pour in the egg mixture and sprinkle with the remaining 1/2 cup of Cheddar cheese.

Finally, bake your quiche in the preheated oven until it's golden brown and fluffy, which should take around 30 minutes. Remove the quiche from the oven and let it cool down for 10 minutes before serving.