Fit the pie crust into a pie or quiche pan. Use a fork to poke small holes all over the crust. Place a sheet of parchment paper into the crust (crumple it a bit to allow it to fit better). Pour dried beans onto the parchment paper. A pound of dried beans will fill a 9 inch pie plate nicely.
Bake the crust in a preheated 350 degree oven for 20 - 30 minutes. The crust should be light golden all over. Do not rush this step; the non-sogginess of the crust depends on it. Remove the crust from the oven. Carefully remove the parchment paper and beans (these will become your official "blind baking" beans). Set the crust aside.
Chop the bacon into thin pieces and cook in a medium fry pan over medium high heat. The bacon should be crisp. Transfer the bacon to paper towels to drain. Remove the drippings from the pan but leave the brown bits of deliciousness.
Add the onions to the fry pan and cook for 4 minutes or so until they begin to soften.
Add the mushrooms and continue to cook another 5 minutes until the mushrooms begin to brown. Add the asparagus and cook for a few more minutes until the asparagus is tender crisp.
Add the reserved bacon bits back to the pan along with the thyme leaves and cook for 2 - 3 minutes more.
Pour the vegetable/bacon filling into the pie crust. Sprinkle the grated cheese on top.
Beat the eggs until the are very thick. Add the cream and milk and beat with a whisk until the mixture is light and fluffy. Add salt and pepper and any other spices or herbs you like.
Place the filled pie crust on a rimmed baking sheet. Carefully pour the custard into the crust stopping when it is filled to the top. You may have a little custard left, but not much.
Place in a 350 degree oven and bake for 30 - 40 minutes. The filling should be puffed and golden and a knife should come out clean when poked in the center.
Remove the quiche from the oven and allow to cool for at least 20 minutes before cutting.
Melt butter in a large saucepan over medium heat. Add the onions and garlic and cook until the onion begins to soften and the garlic is fragrant 3 - 4 minutes. Add the flour and stir to combine. Continue to cook, stirring frequently for another minute or so.
Slowly add the milk, stirring constantly to keep things smooth. Add the tomato sauce and continue to stir. Bring to a boil. Reduce the heat to low and simmer for 5 minutes.
Turn the heat off and slowly add the cheese, stirring until each addition melts. If you make this ahead of time, cover the surface with wax paper so that a crust doesn't form.