Cook the bacon using your preferred cooking method (oven/microwave/stovetop) until very crispy. We prefer to keep it simple by popping them in the microwave, covered, for about 3-4 minutes. Once cooked, transfer to a paper towel lined plate and set aside. Reserve a tablespoon of bacon fat.
Preheat the oven to 350 degrees.
Heat a large skillet over medium high heat and add the tablespoon of reserved bacon fat (* Note 3), mushrooms and onions and cook until golden brown (approx. 3-4 min.)
Add the heavy whipped cream, cream cheese, salt, pepper and thyme and bring to a boil. Stir consistently, until the mixture begins to thicken (approx. 4 minutes). Reduce the heat to medium and cook down until the mixture is thick (approx. 7 minutes).
While cooking the cheese sauce, bring a large pot of water to a boil. Add the green beans and cook until slightly tender (5-7 minutes). Drain and pat dry with a paper towel.
Add the green beans to the cheese sauce and stir until evenly coated.
Transfer to a 8x8 inch pan and cook for 18-20 minutes.
Place the cooked bacon in a food processor and pulse until small crumbs form. Sprinkle the bacon crumbles over the baked casserole and bake for another 5 minutes.
Remove from oven and enjoy immediately for best texture.