Preheat the oven to 375 degrees F. Grease a 7 by 11ņinch casserole dish with the butter and set aside.
Place a 10-inch skillet over medium heat. Once the pan is hot, add the olive oil and the bacon to the pan and cook, stirring often, until most of the fat is rendered and the bacon is browned and crispy, about 8 minutes. Remove the bacon from the pan to drain on paper towels. Add the onions to the pan and saute until translucent, about 3 to 4 minutes. Add the garlic, mushrooms and thyme and cook until the mushrooms have wilted, and most of the liquid has been reduced, about 10 to 12 minutes. Season the mushrooms lightly with salt and pepper. Remove the pan from the heat, and place the mushrooms in a large bowl. Allow the mushrooms to cool completely, and then add the bread.
In a separate bowl, whisk together the cream, milk, and eggs and 1/4 cup of the cheese. Season the mixture with the Essence, the salt, and pepper. Pour the egg mixture over the bread and mushrooms. Fold in the crispy bacon and allow mixture to sit for at least 30 minutes, and up to 2 hours. Once the bread has absorbed most of the custard, pour into the prepared casserole dish and sprinkle the top with the remaining 1/2 cup Parmesan. Bake until golden brown and set in the center, about 35 to 40 minutes.
Yield: 4 to 6 servings