Trim the ends off the fresh green beans and cut them into manageable lengths. Bring a large pot of salted water to a rolling boil and blanch the beans for about 3-4 minutes. Drain and plunge into ice water to preserve color.

In a large skillet, melt 4 tablespoons of unsalted butter over medium heat. Add minced garlic and mushrooms; sauté until softened, about 5-7 minutes. Pour in heavy cream and stir in Parmesan, salt, and pepper. Simmer until thickened, about 5 minutes.

Add the blanched green beans to the skillet and stir well to coat with the sauce. Cook for another 2-3 minutes.

Prepare the fried shallots by thinly slicing and frying in oil until golden, about 3-5 minutes. Drain on paper towels.

Preheat the oven to 375°F (190°C). Transfer the mixture to a greased baking dish, cover with foil, and bake for 20 minutes. Remove foil, sprinkle fried shallots, and bake uncovered for an additional 7-10 minutes until bubbling.

Let the casserole rest for about 5 minutes before serving. Enjoy with your favorite holiday meals!