Pre-heat the oven to 375 degrees F. Grease a 2-quart casserole dish with cooking spray.

Blanch the beans: in a large pot of boiling salted water, add in the green beans and cook for 3 minutes. Work in batches if all of your beans don’t fit in the pot. Drain and set aside while you make the sauce.

Saute the mushrooms: In a large skillet over medium heat, add in the oil. Once hot, add in mushrooms and cook for 5 minutes. Add in 3 tablespoons of butter as well as the thyme. Cook an additional 8 minutes or until the mushrooms are browned and tender. Remove to a plate.

Make the sauce: In the same skillet, melt the remaining 2 tablespoons of butter over medium heat. Once melted, whisk in the flour and then gradually pour in the milk, continuing to whisk until all of the clumps are gone. Simmer over medium hear for 5 minutes until the sauce begins to thicken. Stir in the optional vegan parmesan, garlic, salt and pepper. Cook for 3 additional minutes, stirring often. Remove from heat.

Bake the casserole: Add your blanched green beans to your prepared dish and top with the sauteed mushrooms. Pour the sauce over the top and stir lightly to combine. Cover and bake for 20 minutes. Uncover and bake an additional 15 minutes. Add the onions to the top and bake until the onions are turning a darker brown color, about 3-5 additional minutes.

Serve immediately and ENJOY!