Blanch the green beans

Set the oven to 400°F. Bring a large pot of well-salted water to a rolling boil. Add the green beans and cook for 5 minutes. Drain immediately and plunge them into a bowl of ice water to halt the cooking. Drain once more and set aside.

Build the base for the sauce

While the beans cool, heat the vegan butter or olive oil in a large oven-safe skillet over medium heat. Add the shallot and garlic, season with salt and pepper, and sauté for 2–3 minutes until softened.

Add mushrooms and cook

Stir in the mushrooms along with another small pinch of salt and pepper. Cook for 3–4 minutes, allowing the mushrooms to brown lightly.

Thicken the mixture

Sprinkle the flour over the vegetables and stir so everything is coated. Let it cook for about a minute. Slowly pour in the vegetable broth, whisking constantly to eliminate lumps.

Add almond milk and simmer

Pour in the almond milk and whisk again. Add a little more salt and pepper. Bring the mixture to a simmer, then reduce the heat to low and let it bubble gently for 5–7 minutes until noticeably thickened. Taste and adjust seasoning as needed.

Assemble the casserole

Remove the skillet from the heat. Fold in the green beans and 1/3 of the fried onions (about 1/2 cup). Mix until everything is well coated.

Bake

Scatter the remaining fried onions over the top. Transfer the skillet to the oven and bake for about 15 minutes, or until the casserole is hot, bubbling, and slightly browned.

Store leftovers

Any leftovers will keep in the refrigerator for a few days.