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Green Bean and Potato Casserole

Green bean and potato casserole combines crisp-tender green beans and fork-tender Yukon gold potatoes in a creamy mushroom sauce. Baked under a golden crispy fried onion topping, it makes a hearty, comforting side dish.
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Prep Time 20 minutes
Cook Time 59 minutes
resting 10 minutes
Total Time 1 hour 29 minutes
Servings: 8 servings
Course: Side Dish
Cuisine: American
Calories: 435
Ingredients Equipment Method Notes

Ingredients
  

For the casserole
  • 5 tbsp unsalted butter
  • 8 cups water
  • 1.5 lb green beans fresh, trimmed and cut into 2-inch pieces
  • 1.5 lb Yukon gold potatoes scrubbed and cut into 1-inch pieces
  • 8 oz cremini mushrooms sliced
  • 1 yellow onion small, diced
  • 2 cloves garlic minced
  • 0.25 cup all-purpose flour
  • 2 cups whole milk
  • 1 cup low-sodium vegetable broth
  • 0.5 cup sour cream
  • 1 tsp kosher salt
  • 0.5 tsp black pepper
For the topping
  • 1.5 cups crispy fried onions

Equipment

  • 1 9x13-inch baking dish
  • 1 12-inch skillet

Method
 

Prepare the vegetables
  1. Preheat the oven to 375°F.
  2. Grease a 9x13-inch baking dish with 1 tablespoon of the butter.
  3. Bring the water to a boil in a large pot.
  4. Add the green beans and cook for 4 to 5 minutes, until crisp-tender.
  5. Transfer the green beans to a colander with a slotted spoon.
  6. Add the potatoes to the same pot and simmer for 12 to 15 minutes, until fork-tender.
  7. Drain the potatoes and set them aside with the green beans.
Make the sauce
  1. Melt the remaining 4 tablespoons butter in a 12-inch skillet over medium heat.
  2. Add the mushrooms and onion and cook for 8 to 10 minutes, stirring occasionally, until softened and browned.
  3. Stir in the garlic and cook for 30 seconds.
  4. Sprinkle in the flour and stir for 1 minute.
  5. Gradually whisk in the milk and vegetable broth.
  6. Bring the mixture to a simmer and cook for 3 to 5 minutes, whisking, until thickened.
  7. Remove the skillet from the heat.
  8. Stir in the sour cream, salt, and black pepper.
Assemble and bake
  1. Combine the green beans and potatoes with the sauce.
  2. Spread the mixture in the prepared baking dish.
  3. Bake uncovered for 20 minutes, until bubbling around the edges.
  4. Sprinkle the crispy fried onions over the casserole.
  5. Bake for 5 to 8 minutes, until golden brown.
  6. Let the casserole rest for 10 minutes before serving.

Notes

For the best texture, drain the vegetables well before combining them with the sauce. Refrigerate leftovers for 3 to 4 days; freezing is not recommended because the creamy sauce may change texture. For a dairy-free swap, use dairy-free butter, milk, and sour cream.