Spread the potato slices out and let them cook until browned on one side, about 8 minutes.
Flip them over, add the speck and the fried onion rings to the pan and cook for another 5 minutes. If the pan becomes too dry, add more duck fat to the pan, go ahead.
Season with kosher salt and freshly ground black pepper to taste.
Remove from heat, transfer to a serving platter.
Season the sour cream with kosher salt and freshly ground black pepper and serve on the side.