This is an easy, delicious quiche. Because it is thin and doesn't have a crust, it cooks quickly and evenly. The extra egg yolks and 1/2 & 1/2 give the filling a pleasant richness, and the sweetness of the onions plays nicely against the smoky bacon. If you don't have havarti feel free to use mild cheddar or any other semi-soft cheese.
Preheat oven to 325. Dice up the bacon slices and saute the pieces until they are crispy.
While the bacon cooks, chop the onion into thin slivers. Remove the bacon pieces to a plate, drain off most of the fat, and then caramelize the onion until they're golden brown and sweet. This takes a while, even if you don't cook them until they're mahogany, so read a book or do some dishes while you stir them.
Put the onions and bacon into an even layer on the bottom of a round, 9" pie plate. Whisk eggs, yolks, and 1/2 & 1/2 together and pour evenly over them. Sprinkle the top with grated cheese.
Bake until done. This will take about 25 minutes, but as with all egg dishes, you can't rely on a timer. The middle should be set up. If you give the pan a little poke it shouldn't ripple like the surface of a pond. The easiest way to be sure the quiche is done is to take a knife and make a little cut int he middle. If the filling looks uncooked, give it a few more minutes.
Alternative Cooking Method
Double the recipe, or use a 6" pie pan. Mix half the grated cheese with the onions and bacon. Instead of baking directly on the oven rack, use a water bath. This will result in a thicker quiche that has a velvety smooth texture. Cooking time will increase to 50-60 minutes with this method.