1.5 pounds fresh green beans, rinsed and ends trimmed
2 tablespoons unsalted butter
1 small onion, chopped
2 cloves garlic, minced
2 large portobello mushrooms, chopped
1 teaspoon kosher salt
1/2 – 1 teaspoon freshly ground black pepper, to taste
2 tablespoons all-purpose flour
1 cup chicken broth
1 cup half-and-half
1/2 cup breadcrumbs
6 oz french fried onions
Preheat oven to 375°F. Grease a 9×13 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 7 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!
MAKE AHEAD: Many people over the years have asked how to prepare this recipe ahead of time. I usually prepare it the day before Thanksgiving and refrigerate it (wrapped tightly with foil/saran wrap or a snap on lid) until I am ready to bake it. However, I do not put the breadcrumbs or french fried onions on until right before I bake it so they stay crispy!