Green Bean Casserole From Scratch Recipe

4.96 from 63 votes

Made from scratch with a homemade mushroom soup, this green bean casserole is easy to make with frozen green beans and a few simple ingredients.

Prep Time35

Cook Time25

Total Time1

Cuisine: American

Servings: servings

Preheat the oven to 425°F. Line a large baking sheet with parchment paper.
In a large bowl, toss onions with flour, panko, salt, and pepper. Drizzle olive oil over the mixture and toss again until evenly coated.
Spread onions out in a single layer on the baking sheet and bake for 15–20 minutes, tossing halfway, until golden and crisp. Watch closely near the end to prevent burning.

In a large skillet over medium-high heat, add olive oil and mushrooms. Cook until browned, softened and releasing liquid, about 10 minutes.
Reduce heat to medium, add the onion and garlic, and cook until onions are translucent, about 5 minutes more.
Add milk and bring to a low simmer. In a small bowl, stir together cornstarch and water, then add to the skillet. Stir frequently until thickened. Add the soy sauce, salt and pepper and stir again to combine.

Place the frozen green beans in a 9x13 baking dish. Pour the mushroom mixture over the green beans and stir to coat. Top evenly with the baked crispy onions.
Bake until the casserole is bubbling and the topping is golden, 10–15 minutes. Serve warm.

My Top Tip: Use a mandoline to slice the onions for the topping. For the onions to get crispy, you need them to be sliced really thin. I find this hard to do with a knife and just use my mandoline! Safety tip: always use the mandoline's guard. Also, check the crispy onions often. Because they're sliced so thin, they can burn super fast! I'd check them every minute toward the end of cooking.
Storage: Once your green bean casserole has cooled down to room temperature, transfer any leftovers to an airtight container or cover the baking dish tightly with foil or plastic wrap. Refrigerate it within 2 hours of baking. The casserole will last 3 to 4 days in the fridge! To reheat the casserole you can warm individual portions in the microwave or place the whole dish in a 350°F oven until warmed through.
Make Ahead Directions: You can make the soup up to 4 days ahead of time and keep it covered in the fridge. Don't add it to the green beans until you are ready to bake the casserole so that they stay firm.
Freezing: Make sure to use a freezer-safe baking dish and, after cooling, wrap the dish in a few layers of foil to prevent freezer burn. It'll last 3 months in the freezer! Thaw the casserole overnight in the fridge before reheating.

This recipe has been updated in September 2025 to use a homemade crispy onion topping instead of breadcrumbs (as shown in the recipe video).

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