Preheat oven to 375°F. Grease a 9x13 casserole dish, set aside.
Blanch the beans: In a large pot, bring about a gallon of water and 2 tablespoons of salt to a boil. Add the green beans and boil for 8 minutes. Drain in a colander and immediately plunge the beans into a large bowl of ice water to stop the cooking process. Drain and set aside.
Canned Green Beans: If using canned green beans instead, drain green beans completely and set aside.
Melt butter in a large skillet set over medium-high heat. Add the garlic and onions, stirring occasionally, until the onions begin to soften, about 4 to 5 minutes. Add the mushrooms, salt and pepper and continue to cook for another 1 to 2 minutes.
Sprinkle in the flour and stir to combine. Cook for 2 minutes. Add the chicken broth and stir to combine. Then add the half and half and simmer until the mixture thickens, stirring occasionally, approximately 6 to 8 minutes.
Remove from the heat and stir in all of the green beans. Transfer green bean mixture to prepared casserole dish.
Top with the bread crumbs and then layer the french fried onions on top. Place casserole in the oven and bake until bubbly, about 20 minutes. If your onions start to brown too quickly, cover the casserole with foil. Serve immediately!
Cuisinart Stainless 12-Quart Stock Pot with Strainer Insert
Notes
PREP AHEAD DIRECTIONS: You can prepare the casserole up to 48 hours ahead of time. STOP at step 7 in the directions above. Do not top casserole with the bread crumbs and french fired onions. Instead, wrap cooled casserole tightly with foil, or saran wrap, and store in refrigerator for up to 48 hours.When ready to bake, remove from the refrigerator and let casserole rest at room temperature for 30 minutes (or up to 1 hour) before baking. Then continue on with the recipe directions from step 7.Storage: Store leftovers tightly wrapped in fridge for up to 3 days. You can also store it in the baking dish, just wrap it tightly with plastic wrap or foil.Reheat: For best results, reheat in the oven at 375°F for 15 minutes, or until warmed through. Or, microwave until warm. Adding fresh fried onions on top will make it taste more like it did fresh.Green Beans: For unbeatable flavor and texture, use fresh green beans. The next best choice is frozen green beans, prepare them just as you would fresh. To use canned green beans, use 6 cans of green beans, well drained.Nutmeg: 1/4 to 1/2 teaspoon of ground nutmeg can be added to the cream sauce for a surprising warmth and depth of flavor.Cheese: Add up to 2 cups of shredded cheese to the green bean mixture. Or sprinkle on top of the casserole before breadcrumbs and fried onions. Try sharp white cheddar, shredded parmesan cheese, fontina, or sharp cheddar.Not a Mushroom Fan? Nix the mushrooms and double the onion in the cream sauce to create a homemade cream of onion sauce instead!