• Preheat oven to 350 degrees Fahrenheit.

Cook the green beans

• Set a large pot 1/2 full of water over high heat and bring to a boil. Add a couple of generous pinches of salt and then the trimmed and cut green beans. Return to a boil and cook until tender, 5 minutes for beans with a bit of a bite, 6 minutes for beans that are more cooked. If you're cooking the casserole right away, you can strain the beans into a colander and set aside. If the beans are going to be sitting for a while and/or you're prepping for a make-ahead situation, dunk the beans into an ice bath first to stop them from overcooking. Fill a large bowl full of cold water and add a handful of ice cubes. Transfer beans to the bowl and let sit for a minute or two until cold. Drain water.

Make the sauce

• Set a large saute pan or a stock pot over medium-low heat. Add 4 tablespoons (1/4 cup) of the vegan butter. When melted, add the onion, mushrooms, 1/2 teaspoon dried thyme, 1/2 teaspoon salt, and 1/4 teaspoon pepper. Cook, stirring occasionally, until onions and mushrooms are tender and much of the liquid from the mushrooms has cooked off, about 5 minutes.
• Add the sherry and cook, stirring constantly, until evaporated, about 1 minute.
• Add the flour and continue to cook, stirring constantly, for 3 minutes. If the flour begins to really stick to the bottom of the pan, add a splash of the vegetable broth to help loosen it and keep it from burning.
• Slowly pour in the vegetable broth and then the almond milk and soy sauce, stirring constantly, scraping up any bits from the bottom of the pan. Increase heat to medium-high and cook, stirring frequently, until the sauce is thickened and bubbling. Remove the sauce from the heat.

Assemble the casserole

• Stir the green beans into the sauce, tossing until coated. Taste green bean mixture and add more salt and pepper, if desired.
• Pour the green bean and sauce mixture into a 2-quart casserole dish. Sprinkle crispy onions evenly over the top. Melt the remaining 1 tablespoon of vegan butter then drizzle over the top of the onions.

Bake the casserole

• Cover with foil and bake until bubbling, 20-25 minutes. Remove the foil and continue baking until the crispy onions are toasty and golden, about 5 more minutes. Remove from oven and serve!