16 ounces fresh green beans, plus olive oil for sautéing
8 ounces sliced (and washed) mushrooms
1 cup heavy cream
3 cups freshly shredded gruyère
2 cups crispy fried onions
In a large skillet, combine the green beans and mushrooms, and add about 1 tablespoon of olive oil. Sauté the vegetables on medium-low heat for 5-7 minutes to cook them down and help remove the water.
Preheat the oven to 350. Remove the veggies from the skillet, and place them into an oven-safe dish; season the vegetables with salt and pepper. In the same skillet, add the heavy cream, and let it heat on low for about 2 minutes. Then, slowly add in the cheese, whisking until it fully melts into the cream. Heat the cheese sauce on low for 5 minutes, then let it sit for 5 minutes to thicken.
Pour the cheese sauce over the vegetables, and lightly stir the vegetables to combine them with the sauce. Bake 15 minutes at 350 or until the green beans are tender. Then, remove the casserole from the oven, and top it with the fried onions. Place the casserole back into the oven, and cook it for an additional 10 minutes or until the onions are toasted.