Preheat the oven to 400 degrees F and lightly grease a 9x13-inch casserole dish.
Thinly slice the potatoes into ⅛-inch rounds. I like to keep the peels on for nutrition and time-saving reasons, but you’re welcome to peel them first. If you have a mandolin or food processor attachment, that’ll save time.
In a large pot over medium heat, melt the vegan butter. Whisk in the flour and stir until the sauce thickens and becomes a roux, about 3 to 5 minutes.
Whisk the plant-based milk and vegetable broth into the roux. Stir in the nutritional yeast, garlic powder, onion powder, and salt until the sauce thickens, about 5 to 8 minutes.
Layer half of the potatoes in the casserole dish, pour half of the sauce spreading evenly over the potatoes and allowing it to seep through the cracks. Layer the rest of the potatoes and spread the rest of the sauce over them evenly. Cover with tin foil and bake for 25 minutes.
Uncover the casserole and bake for another 35 minutes.
If you’re wondering why this recipe has this singular name, we are happy to clarify. Originally from England, this recipe is called Vegan Scalloped Potatoes because of the way this vegetable is sliced. It is basically very thinly sliced, which means not only that the potatoes are cooked faster but that the creamy mixture can enter the many layers and therefore, lets the flavor in everywhere.