Vegan Green Bean Casserole

Ingredients

• Kosher salt
• 1 1/2 pounds green beans, trimmed and cut into 2-inch lengths
• 1 medium yellow onion, roughly chopped
• 1/2 pound button or cremini mushrooms, stems trimmed
• 3 cups vegetable stock or low-sodium broth, plus more as needed
• One head cauliflower, cored and cut into medium florets
• 3 tablespoons extra-virgin olive oil
• 1 tablespoon nutritional yeast
• 1 teaspoon garlic powder
• 1 teaspoon fresh thyme leaves or 1/2 teaspoon dried thyme
• Finely grated zest of 1 lemon, optional
• Freshly ground black pepper
• Canola oil or other neutral oil, for frying
• 1 large red onion, halved and thinly sliced into half moons

Directions

1. Pour water into a large saucepan until it is about halfway full, and bring it to a boil. Salt the water well, add the green beans, and cook for about 6 minutes, until they are just tender. Drain the beans, then wash out the saucepan.
2. Add the yellow onion and mushrooms to a food processor and pulse about 15 times, until finely chopped. Scrape the mixture into a large bowl, then wash the food processor bowl.
3. In the saucepan you used for the beans, warm the vegetable broth over medium heat until it simmers. Lower the heat to medium-low, add the cauliflower, and cover the pan. Cook for about 10 minutes, until a knife slides into the cauliflower very easily. If you see steam escaping from beneath the lid, turn the heat to low; you want the cauliflower to soften while keeping as much broth in the pan as possible.
4. Move the cauliflower and its cooking liquid into the cleaned food processor bowl, and let it cool a little. Process until the mixture is extremely smooth. A high-powered blender will make the silkiest sauce, if you have one, but a food processor can get there too if you let it run for a full minute or longer and stop to scrape the sides now and then.
5. Set the oven to 350 degrees F (180 degrees C). Wash the saucepan once more, then dry it thoroughly. Add the olive oil and warm it over medium heat until it shimmers. Tip in the mushroom-onion mixture and season generously with salt. Cook, stirring often, for about 10 minutes, until the vegetables are tender and have stopped giving off liquid.
6. Stir in the cauliflower sauce, nutritional yeast, garlic powder, thyme, and lemon zest, if using, then season with salt and pepper. This is not the moment for timid seasoning. Fold in the green beans. If the sauce feels thicker than you’d like, loosen it with additional broth until the texture looks right to you. Transfer everything to a 2-quart baking dish.
7. Bake for 25 to 30 minutes, until the casserole is hot and bubbling.
8. Meanwhile, pour canola oil into a medium saucepan to a depth of 1/2 inch and heat it until a piece of red onion bubbles when it hits the oil. Add half of the sliced red onion and fry, stirring from time to time, until golden brown, 9 to 10 minutes. Lift the onions out with tongs or a spider and set them on a paper towel-lined plate. Season generously with salt. Fry the remaining red onions the same way. Once the onions are cool enough to handle, gently fluff them with your hands so they crisp.
9. Rest the casserole for about 5 minutes, then top it with the fried onions and serve.