In a large skillet, melt butter with olive oil. Add mushrooms and sauté for 10 minutes. Add shallot and garlic and cook until fragrant, about two minutes. Add thyme and parsley and sauté another 10 minutes. Season with salt and pepper to taste.

Preheat oven to 350 degrees Fahrenheit. Just before serving, place the brie in the oven for five to eight minutes. To serve, transfer to plate. Spoon mushrooms on top and sprinkle with chives and fresh parsley. Finish with a drizzle of truffle oil and serve alongside toasted crostini.