A creamy, dairy-free vegan green bean casserole made with fresh green beans, a coconut milk mushroom sauce, and a crunchy fried onion topping. Make-ahead friendly and perfect for Thanksgiving!
Melt the butter in a large pot over medium-high heat. Add the mushrooms, garlic, salt, and pepper. Cook until the mushrooms release their liquid and it fully evaporates, about 25–30 minutes.
Stir in the flour and cook 1 minute.
Slowly pour in the vegetable broth while stirring. Bring to a simmer.
Stir in the coconut milk, reduce heat to low, and cook until the sauce is thickened and reduced, around 12 minutes. Taste and adjust seasoning.
Blanch the Beans
Heat oven to 400°F.
Fill a large bowl with ice water.
Bring 4 quarts of water to a boil. Add the salt and all 36 oz green beans. Cook until bright green and crisp-tender, about 6 minutes.
Drain and immediately plunge into the ice water.
Spread the beans on paper towels to dry completely.
Make the Topping
Pulse the sourdough cubes, butter, salt, and pepper in a food processor until coarse crumbs form.
Transfer to a bowl and mix in the fried onions.
Combine & Bake
Stir the green beans into the sauce until fully coated.
Transfer to an 11×14-inch baking dish. The dimensions don't need to be exact so long as it can hold 4 quarts.
Sprinkle the topping evenly over the surface.
Bake until the sauce is bubbling around the edges and the topping is golden brown, about 15 minutes.