📖 Instructions

1. Prep the Green Beans: Begin by washing 1.5 pounds of fresh green beans. Trim off the tough stem ends; you can snap them by hand or use a knife. For a nice presentation and easier eating, snap or cut any particularly long beans into 2-inch pieces.
2. Blanch the Green Beans: Bring a large pot of salted water to a rolling boil. Carefully add the trimmed green beans and blanch them for 3-4 minutes. You want them to be bright green and crisp-tender, not mushy. Immediately drain the beans and plunge them into an ice bath for 2-3 minutes to stop the cooking process and preserve their vibrant color. Drain thoroughly again and set aside.
3. Prepare the Mushrooms: Clean 1 pound of cremini mushrooms by wiping them with a damp cloth or a mushroom brush. Avoid rinsing them under water, as they absorb moisture easily. Slice the mushrooms evenly, about 1/4 inch thick.
4. Sauté the Aromatics: In a large, heavy-bottomed skillet or Dutch oven, melt 4 tablespoons of unsalted butter over medium heat. Add 1 large finely diced yellow onion and sauté for 5-7 minutes, until softened and translucent. Add 2 cloves of minced garlic and cook for another minute until fragrant. Don't let the garlic brown.
5. Cook the Mushrooms: Add the sliced mushrooms to the skillet. Increase the heat slightly to medium-high. Cook, stirring occasionally, for 8-10 minutes, or until the mushrooms have released their liquid and browned nicely. This browning develops deep, savory flavor.
6. Make the Roux: Sprinkle 1/4 cup of all-purpose flour over the sautéed onions and mushrooms. Stir constantly for 1-2 minutes, cooking out the raw flour taste. This mixture will become thick and pasty – this is your roux, which will thicken the sauce.
7. Build the Cream Sauce: Gradually whisk in 2 cups of whole milk and 1/2 cup of chicken or vegetable broth (or just more milk if you prefer). Pour slowly, whisking continuously to prevent lumps. Bring the sauce to a gentle simmer, stirring frequently, until it thickens. This usually takes about 5-7 minutes.
8. Season the Sauce: Reduce the heat to low. Stir in 1 teaspoon of Worcestershire sauce (optional, but adds a nice umami kick), 1/2 teaspoon of dried thyme, 1/2 teaspoon of salt, and 1/4 teaspoon of black pepper. Taste and adjust seasonings as needed. If the sauce is too thick, add a splash more milk or broth until it reaches your desired creamy consistency.
9. Combine and Assemble: Preheat your oven to 375°F (190°C). Gently fold the blanched green beans into the mushroom cream sauce until they are fully coated. Pour the mixture into a 9x13 inch baking dish.
10. Bake the Casserole: Bake the casserole uncovered for 20-25 minutes, or until the sauce is bubbly and the green beans are heated through.
11. Add Crispy Onions: Remove the casserole from the oven. Evenly sprinkle 1.5 cups of crispy fried onions over the top.
12. Final Bake: Return the casserole to the oven and bake for another 5-10 minutes, or until the fried onions are golden brown and perfectly crispy. Keep a close eye on them to prevent burning!
13. Serve: Let the casserole rest for a few minutes before serving hot. Enjoy your wonderfully homemade green bean casserole!