Heat the oil in a cast-iron pan over medium heat.
When the oil is hot add the grated potato and onion. Sprinkle generously with salt & pepper and stir to combine.
Cook, stirring occasionally, until potatoes and onion begin to brown, about 10 minutes.
Stir in the Parmesan cheese until well combined. Form the mixture into a disk shape and cook until the bottom is browned, about 3 minutes.
Flip onto a plate and serve.
