Katie Lee's green bean casserole recipe is a classic version of the Thanksgiving fave, made with fresh ingredients in place of canned soup.
Tip: Blanching the green beans will help them keep their bright green color.
Swap options: For a lighter dish, use whole milk in place of the half-and-half. Try cheddar cheese instead of Parmesan.
Preheat oven to 350° F. Coat a 9 x 13 casserole dish with nonstick cooking spray.
Bring a large pot of salted water to a boil. In the meantime, prepare an ice water bath by filling a large bowl with cold water and ice. Cook green beans in the boiling water for 3 to 4 minutes, until tender. Drain and immediately submerge in ice water bath to stop the cooking. Drain.
In a large skillet, melt butter over medium heat. Add onion and cook until translucent, stirring often, about 8 minutes. Stir in mushrooms and cook 7 to 8 minutes. Add the flour and continuously stir for 2 minutes. Whisk in half-and-half, salt, and pepper. Continue to stir until the mixture begins to coat the back of a wooden spoon. Turn off the heat and whisk in parmesan and vinegar. Toss the green beans in the mixture until evenly coated and transfer to prepared baking dish.
Bake for 20 minutes. Remove from oven and top with fried onions. Bake for an additional 5 minutes and serve.