Add the white wine and cook until wine is reduced.
Add the water, nutritional yeast and arrowroot powder. Bring to a simmer and cook 5-10 minutes until the mixture has thickened and the the vegetables are tender.
For the sweet potato topper
Fill a medium saucepan with water to completely cover the peeled sweet potatoes.
Cook on low until tender to the center (about 20-30 minutes).
Drain and mash the sweet potatoes with a whisk (it's quite easy actually).
Season with salt and pepper to taste and a splash of unsweetened almond milk if desired.
To assemble the shepherd's pie
Pre-heat the oven to 350 F.
Place the filling in an oven safe 9" x 9" baking dish. Top with a layer of the mashed sweet potato.
Place the dish uncovered in the oven for 15-20 minutes or until the center is hot and the sweet potato topping is gently browned.
Recipe by Plant Craft at https://www.rachelcarr.com/celery-root-mushroom-shepherds-pie/