Let your refrigerated pie crust sit on the counter for 15 minutes to come to room temperature.
Preheat your oven to 375 degrees.
Add the butter and olive oil to a frying pan over medium high heat. Once the butter is melted, add your finely chopped onion and cook until golden brown and translucent, about 105 minutes. Set aside.
Gently unroll the pie crust, roll out with a rolling pin just a little to seal any cracks, and transfer to a 9" round pie dish. Press the crust in to the pan on the bottom and sides then tuck any additional crust under the edges and crimp around the edge as desired.
In a mixing bowl, whisk the eggs until a lighter yellow color. Wisk in the heavy cream, half and half, Dijon mustard, dried parsley, salt, pepper and nutmeg. Set aside.
Spread the cooked chopped bacon evenly over the crust, sprinkle 1/2 cup of each of the cheeses over the bacon, pour egg mixture all over the bacon and cheese, then sprinkle remaining 1/4 cup of each cheese over the top.
Place your quiche in the oven on the middle shelf, bake for 40-45 minutes until golden brown. (Note, it will puff a bit in the oven, but then deflate again once you take it out and let it cool, so don't stress.)
Remove from oven and let cool on a cooling rack for at least 10-15 minutes before slicing and serving. (Leftovers can be kept in the refrigerator and served cold or reheated in a 325 degree oven for about ten minutes.)