01 -
First things first, get those green beans ready. Trim the ends, give 'em a good wash. I always blanch mine in salted boiling water for about 5 minutes, just until they're bright green and tender-crisp. Then, immediately plunge them into an ice bath to stop the cooking. This is where I always forget to salt the water, honestly, but it makes a difference! Drain them really well; excess water is the enemy of a good casserole.
02 -
In a large saucepan, melt a tablespoon of butter over medium heat. Toss in your sliced mushrooms and let them cook until they're golden brown and all their liquid has evaporated. This step adds so much flavor, don’t skip it! I remember one time, I didn't cook them long enough, and the casserole ended up a bit watery. Oops, learned that the hard way. Set them aside for a moment.
03 -
In the same saucepan, melt the remaining butter. Whisk in the flour and cook for about a minute, stirring constantly, until it forms a pale roux. It should smell a little nutty, a bit like popcorn. Slowly, and I mean slowly, whisk in the milk and chicken broth. Keep whisking until the sauce thickens and is smooth. This is where patience pays off; lumps are no fun, trust me.
04 -
Stir in the garlic powder, onion powder, salt, and pepper into your creamy sauce. Taste it! Does it need more salt? More pepper? This is your chance to adjust. Then, gently fold in your blanched green beans and sautéed mushrooms. The sauce should coat everything beautifully. It just smells like pure comfort at this stage, honestly!
05 -
Pour the green bean mixture into a 9x13 inch baking dish. I usually give the dish a light spray with cooking oil first, just to be safe. Pop it into a preheated oven at 375°F (190°C) for about 20-25 minutes. You want the casserole to be bubbly and heated through. This is the base, and we're not adding the star topping yet, remember? We need to keep fried onions crunchy!
06 -
Now for the grand finale! Once the casserole base is bubbly and hot, take it out of the oven. Sprinkle those crispy fried onions evenly over the top. Return it to the oven for just 5-7 more minutes, or until the onions are golden brown and perfectly crisp. Watch them closely – they can burn fast! This short, final bake is the ultimate secret to keep fried onions crunchy, not soggy. Serve immediately!