Preheat the oven to 375 degrees F.
Prepare the pie dough
as directed and press the dough into a 9-inch pie tin, forming a fluted edge. Set aside in the refrigerator as you prepare the quiche
Set a 12-inch saute pan over medium heat, and add the bacon. Cook the bacon, stirring often, until most of the fat has rendered and the meat is crispy, about 5 to 7 minutes. Remove the bacon from the pan and drain
on a paper-lined plate. Add the onions to the pan and cook, stirring occasionally, until the onions
are wilted, and lightly caramelized, about 8 minutes. Add the mushrooms, thyme, and garlic
to the pan and season with the salt and pepper. Cook the onions and mushrooms, stirring occasionally, until most of the moisture has cooked out of the mushrooms and they are caramelized, 8 to 10 minutes. Remove the pan from the heat and allow the onions and mushrooms to cool for 10 minutes before placing in the reserved pie tin
with the rendered bacon.
In a medium bowl, combine the heavy cream
and eggs and whisk
. Pour the cream mixture over the onion mixture, and sprinkle the cheese
over top. Place the pie tin on a sheet pan and place in the oven. Bake until golden brown, and the custard
has set, 35 to 40 minutes. Be sure to rotate the sheet pan
after 15 to 20 minutes to ensure even browning.