📖 Instructions

1. Before you even think about mixing things, get your oven ready. Preheat it to a cozy 375°F (190°C). This ensures your casserole bakes evenly and those crumbs get perfectly golden. While the oven is warming, grab a 9x13-inch baking dish; you'll want to lightly grease it with butter or cooking spray to prevent any sticking. Nothing worse than a casserole stuck to the bottom!
2. Now for the green beans! If you're using fresh green beans, you’ll need to do a little prep. First, rinse them really well under cold water. Next, 'snap' or trim off those tough ends. You can do this by hand or with a knife. After trimming, cut the longer beans into bite-sized pieces, roughly 1 to 1.5 inches long. Once trimmed, bring a large pot of salted water to a rolling boil. Add your prepared green beans and blanch them for about 4-5 minutes. You're looking for them to be bright green and slightly tender-crisp, not mushy. Immediately drain the beans and plunge them into an ice bath (a bowl of ice water) to stop the cooking process and preserve their vibrant color. After a few minutes, drain them thoroughly and set aside. If you're using frozen green beans, simply thaw them according to package directions and drain any excess water. Canned green beans are another option, but make sure to drain them *very* well.
3. Time to make the dreamy cream sauce! In a large saucepan or Dutch oven, melt 1/4 cup (4 tablespoons) of unsalted butter over medium heat. Once it's shimmering, sprinkle in 1/4 cup of all-purpose flour. Whisk constantly for 1-2 minutes until it forms a smooth paste, or roux. This little step is crucial for thickening your sauce. Make sure to cook out the raw flour taste; it should smell slightly nutty. Gradually, and I mean *gradually*, pour in 2 cups of whole milk while whisking vigorously to prevent lumps. Nobody wants lumpy sauce! Once all the milk is incorporated, continue to whisk and cook over medium heat until the sauce thickens to your liking. It should be thick enough to coat the back of a spoon, which usually takes about 5-7 minutes. If it gets too thick, add a splash more milk. If it's too thin, let it simmer a little longer.
4. Let's flavor this beautiful sauce! Remove the saucepan from the heat. Stir in 1/2 teaspoon of garlic powder, 1/4 teaspoon of onion powder, 1/2 teaspoon of salt, and 1/4 teaspoon of black pepper. Give it a good taste. Does it need more salt? A pinch more pepper? Adjust to your preference! This is where you make it *your* perfect sauce. Now, for a touch of richness, stir in 1/2 cup of grated Parmesan cheese. The Parmesan adds a lovely salty, umami depth that elevates the entire dish. Finally, gently fold in your blanched and drained green beans until they are fully coated in the creamy sauce.
5. Pour this delicious green bean mixture into your lightly greased 9x13-inch baking dish. Spread it out evenly. At this point, the kitchen probably smells amazing, but we're not done yet!
6. Now for the star of the show: that buttery crumb topping! In a medium bowl, combine 1 cup of panko breadcrumbs, 1/2 cup of freshly grated Parmesan cheese, 1/4 cup of all-purpose flour, and 1/4 teaspoon each of garlic powder, onion powder, salt, and black pepper. Use a fork or your fingers to mix everything together really well. Then, pour in 4 tablespoons of melted unsalted butter. Toss everything together until the breadcrumbs are evenly moistened and clumpy. This is going to give you that incredible texture and flavor. If you find your topping is a little dry, add another tablespoon of melted butter.
7. Generously sprinkle the buttery crumb topping evenly over the green bean mixture in the baking dish. Make sure every inch is covered! Press it down ever so slightly with the back of a spoon or your fingers.
8. Pop the casserole into your preheated 375°F (190°C) oven. Bake for 25-30 minutes, or until the sauce is bubbly around the edges and the crumb topping is beautifully golden brown and crispy. Keep an eye on it during the last 10 minutes to make sure the topping doesn't get *too* dark. If it starts browning too quickly, you can loosely tent it with aluminum foil.
9. Once it's done, carefully remove the casserole from the oven. I know it's tempting, but let it rest for about 5-10 minutes before serving. This allows the sauce to set a bit, preventing it from being too runny when you scoop it out. Serve it warm and watch it disappear!