If using fresh green beans, blanch them in boiling water for 3-4 minutes until they're bright green and slightly tender-crisp. Immediately transfer them to an ice bath to stop the cooking process. Drain well. If using canned or frozen green beans, drain them well and set aside.

In a large skillet, melt the butter over medium heat. Add the chopped onion and cook until softened, about 5 minutes. Add the minced garlic and cook for another minute until fragrant.

Add the sliced mushrooms to the skillet and cook until they're softened and have released their moisture, about 8-10 minutes.

Sprinkle the flour over the mushroom mixture and cook for 1 minute, stirring constantly. Gradually whisk in the chicken broth and milk until smooth. Bring to a simmer, then reduce heat and cook until the sauce has thickened, about 5-7 minutes. Stir in the soy sauce and Worcestershire sauce. Season with salt and pepper to taste.

Preheat oven to 350°F (175°C).

In a large bowl, combine the green beans and the mushroom sauce. Stir to coat.

Pour the mixture into a 9x13 inch baking dish.

Sprinkle 1 cup of the crispy fried onions evenly over the top of the casserole.

Bake for 20-25 minutes, or until the casserole is heated through and the onions are golden brown.

Sprinkle the remaining ½ cup of crispy fried onions over the top of the casserole during the last 5 minutes of baking. This prevents them from burning.

Let the casserole rest for 5-10 minutes before serving. This allows the sauce to thicken slightly.

To make homemade crispy fried onions: Separate the onion slices into rings. In a bowl, combine the flour, salt, and pepper. Dredge the onion rings in the flour mixture, making sure they're evenly coated. Heat about 2 inches of vegetable oil in a large pot or deep fryer to 350°F (175°C). Carefully add the onion rings to the hot oil in batches, being careful not to overcrowd the pot. Fry for 2-3 minutes, or until the onions are golden brown and crispy. Remove the onions from the oil with a slotted spoon and place them on a paper towel-lined plate to drain excess oil. Season the onions with a little extra salt, if desired. They're best served immediately!