1. Prepare the oven and preheat it to 200 degrees C or 400 degrees F.
2. Roll out the pie crust, then place it into a deep-dish pie plate. Press the sides of the crust to the plate. Put it in the fridge while you prepare the rest of the ingredients.
3. Place a large skillet on the stove and turn the heat to medium-low. Add butter and allow it to melt.
4. Add the onions into the hot skillet, then sauté for about 20 minutes or until they turn golden brown. Remove from the skillet and transfer them into a mixing bowl.
5. In the same skillet over medium-high heat, add the bacon slices and cook for a few minutes until crispy. Transfer them onto a clean plate lined with paper towels to drain excess grease. Move it into the bowl with the onions.
6. Add eggs, salt, pepper, and cream into a mixing bowl. Beat until well blended. Transfer the mixture into the bowl with the caramelized onions and bacon. Add the grated cheese as well and stir everything until well combined.
7. Transfer the mixture to the prepared crust and spread it evenly. Cover with foil.
8. Place it in the preheated oven and bake for about 45 minutes. Remove the cover and bake for 15 more minutes or until the top turns golden brown.
9. Remove the quiche from the oven and allow it to rest for about 15 minutes at room temperature. Slice into even servings.
10. Serve and enjoy!

Notes:

• Place any leftovers in an airtight container, then put them in the fridge. They can last up to 3 days or 3 months in the freezer. Reheat for a few minutes before serving again.