Spiralize 1 potato using the shredder or julienne blade. Place in greased deep 3 quart casserole. Drizzle with a little olive oil and season liberally with salt and pepper. Drizzle with 1/8 cup heavy cream. Add 1/2 of cheese.
Top potato with cooked onions. Spiralize the second potato and place on top of onions. Repeat as first potato, drilling with oil, cream and seasoning. Top with remaining cheese.
Cover dish and refrigerate until baking if desired.
Bake covered at 400 for 30 minutes. Remove cover and continue baking until top is golden and a knife inserts easily, about 20-30 minutes.
Garnish with green onion tops, rosemary or parsley
Notes
*it is easier to spiralize a whole onion than a half of one, so go ahead and do the whole onion and reserve the rest for another use.