Preheat oven to 350 degrees F.

Blanch Green Beans: Bring a large pot of water to a boil. Blanch the green beans until they’re bright green and tender-crisp, about 3 minutes. Drain into a colander and set aside. (Don't overcook them!)

Sauté mushrooms and shallot: Add 2 tablespoons olive oil and 2 tablespoons butter to a large skillet over medium-high heat. Add mushrooms and cook, stirring only occasionally, for 5-8 minutes. Add shallot and cook for 2-3, until tender. Add garlic and cook for 30 seconds.

Finish sauce: Reduce heat, move mushrooms and onions to the side of the pan. Add remaining 2 tablespoons butter and allow to melt. Stir in flour and cook for 1 minute. Slowly whisk in chicken broth and then milk until smooth and bring to a simmer over medium heat, stirring everything in the pan together. Season with cracked black pepper. Cook for a few minutes, until sauce thickens. Remove from heat and stir in cream and shredded cheese, (if using). Taste and add additional pepper, and salt if needed.

Add green beans back to pan and toss to coat.

Bake: Use the (if oven safe) dish you've been cooking with or transfer mixture to a greased casserole dish. Top with crispy onions. Bake at 350 degrees F for 30-35 min or until hot and bubbly and green beans are tender (keep in mind they will continue to cook out of the oven).