1 1/2 cups paper thin onion slices
1 pound Yukon Gold potatoes, peeled and grated ( Do not substitute any other potato )
1 tsp salt, divided
2 Tbls unsalted butter, melted
Preheat oven to 425 degrees F. ( I think 400 degrees F would be better). Butter large rimmed nonstick baking sheet. Place onion in large bowl. Toss potatoes with 1/2 teaspoon salt in medium bowl. Let stand 5 minutes. Using hands, squeeze out excess liquid from potaotoes. Add potatoes, 1/2 teaspoon salt, and melted butter to onion. Toss to coat.
Divide mixture into 4 mounds on prepared baking sheet, spacing apart. Roast 15 minutes, then turn mounds over with spatula, pressing down to flatten to 4-inch-diameter rounds (cakes will still be soft). Reduce oven temperature to 350 degrees F, bake until cakes are golden and crisp around edges, about 45 minutes longer.
You could also make these smaller,dice the onion, and serve them as an appetizer topped with sour cream and smoked salmon. Adjust the cooking time accordingly.