Take the dish you're going to bake the scalloped potatoes in and cut a piece of foil large enough to cover the top of the dish (9.5 in. pie dish used in the picture above). Butter one side of the foil, leaving a seam allowance around the edge of the foil (this will get crimped around the pan so there is no need to waste butter here).
Scrub the potatoes and peel them. Using a mandoline or a very sharp chef's knife, slice potatoes crosswise into 1/4 in. thick rounds (or the thin setting on the mandoline).
Add the sliced potatoes into a large bowl with the salt, cayenne pepper, and black pepper; toss to combine (get in there and make sure every potato has seasoning).
Place the pie dish (preferably) in front of you and make one strip of overlapped potatoes (each potato overlapping about 2/3 of the next) in the upper 1/3 of the dish. Repeat by making another strip of potatoes beneath the first strip, making sure the second row overlaps halfway over first row.
Gently push both rows of potatoes toward the top edge of the dish. They will slide up the sides of the dish and create a steep diagonal. Make sure the potatoes are snug enough that they hold their shape in the dish, but not too snug or they won't cook evenly.
Make another row of potatoes like before, pushing each row up to meet the last until the dish is full. If you have any potato slices left over, tuck them into any available slots.
Line a baking sheet with foil and place the pie dish on it.
To make the non-dairy heavy cream, combine the non-dairy milk, oil, and salt in a blender and blend for 30 seconds. Pour the mixture over the potatoes. Top with both cheeses and cover the dish with the buttered foil, butter side down. Crimp the edges tightly so steam doesn't escape!
Bake for 60-90 minutes. You'll know when the scalloped poatoes are done when the potatoes in the middle of the pie dish are tender.
Remove the potatoes from the oven and turn on the broiler. Remove the buttered foil and place the potatoes under the broiler.
Broil until the cheese is bubbly and brown. DO NOT GO ANYWHERE. This process can go from 0 to 100 real fast. Just watch them as they brown. It'll be well worth the wait.
Let cool for 15 minutes. Bottoms up!
For the potatoes:
3 lb. russet potatoes
1-1 1/2 tbsp salt crystalsor 2-3 tsp kosher salt
1/2 tsp cayenne pepper
1/ tsp ground black pepper
For the non-dairy heavy cream:
1 C non-dairy unflavored milk
1/2 C canolaorvegetable oil
1/2 tsp salt
For the topping:
Room-temperature unsalted butter OR vegan butter (for the foil part of the instructions)
3.5 oz non-dairy cheddar shreds (get the kind that melts like Violife or Daiya)
3.5 oz non-dairy parmesan (this recipe used Violife because it melts)