8ouncesfresh sliced mushrooms( like cremini, shiitake, or button)
2teaspoonsfresh thyme leaves
1cuplow-sodium chicken broth
salt and black pepper(to taste)
½cupcrispy French fried onions
Bring a pot of water to a boil and salt generously. Add green beans and cook for 3-4 minutes. Drain and add the beans to a bowl of ice water to stop the cooking. Cool, drain well, and set aside.
In a large skillet, melt butter over medium heat and add the onions. Cook, stirring occasionally, until softened, 8-10 minutes. Add thyme and season with salt and pepper.
Continue cooking and stirring occasionally until the onions have turned golden brown. This will take 30-40 minutes. If the onions start to dry out, add 1-2 tablespoons of water as needed. Set aside.
In a large skillet over medium heat, cook the bacon until brown and crisp.
Transfer to a paper towel-lined plate and set aside. Drain the bacon grease, leaving 2 tablespoons in the pan.
Add the mushrooms to the bacon drippings in the pan. Cook, stirring occasionally, until tender and caramelized. Stir in the fresh thyme leaves and season to taste with salt and pepper.
Reduce the heat to medium-low. Add 2 tablespoons of butter to the skillet. When melted, add the flour and whisk to incorporate. Cook for 1-2 minutes.
Slowly pour in the chicken broth, then the milk, whisking to incorporate. Simmer to thicken the sauce. Season to taste with salt and pepper.
Add half of the shredded cheese and whisk until melted and fully incorporated. Stir in the caramelized onions.
Transfer the green beans to the baking dish. Pour the sauce over the beans. The casserole can either be baked immediately or refrigerated to bake at a later time.
To Bake Immediately
Top the casserole with the remaining bacon and cheese and French- fried onions. Cover and bake at 375 degrees for 15 minutes. Uncover and bake another 5 minutes until bubbly and brown around the edges.
To Bake Later
Cool and cover the casserole with plastic wrap and refrigerate. When ready to bake, let the casserole come to room temperature and preheat the oven to 375 degrees. Top with the remaining bacon and cheese and French-fried onions. Cover and bake for 15 minutes. Uncover and bake for another 5 minutes until brown and bubbly.
Use fresh ingredients for optimal flavor and texture.
Use freshly shredded cheese for the best melting quality.
To make the casserole ahead of time (2-3 days in advance), prepare it according to the recipe, adding the beans and sauce to the baking dish. Cool, cover, and refrigerate. When ready to bake, top with cheese, bacon, and fried onions. Cover and bake per the recipe directions.
To prevent the casserole from turning mushy, avoid overcooking the beans. Add the beans to boiling water for a few short minutes, then transfer to ice water to stop the cooking. This leaves the beans with just enough firmness to bake up perfectly in the casserole. Additionally, add the cheese, bacon, and fried onions on top right before baking. This prevents the topping from getting soggy.
Canned and frozen green beans can be substituted for fresh, but they will not have the same crisp-tender texture. To use canned green beans, drain and add directly to the baking dish. To use frozen beans, thaw and drain, then add directly to the baking dish.