Prep the potatoes and onion. I used 5 medium potatoes for the 1 kilo and used a mandoline to slice the potatoes and onion.
Preheat your oven to 190° C (375° F), grease a large pie dish with butter. Sprinkle ½ the garlic in the pie dish. I used a 9 inch pie dish.
Add ½ the potatoes overlapping the slices.
Add ½ the onion slices on top of the potatoes, and sprinkle with salt and lightly with pepper, as desired.
Sprinkle ½ of the shredded cheese over the onion.
Repeat the layers starting with the remaining garlic, then potatoes, onion, salt and pepper. Add the sour cream, whipping, or milk, or any combination of these evenly over the top. I used ½ cup sour cream then added milk to bring it to ⅔ cup.
Sprinkle remaining shredded cheese over the top, then sprinkle on the Parmesan cheese.
Cover the dish with foil and bake for 30 minutes. Then uncover and bake for 30 minutes more.
Slice into wedges, serve as a side dish, enjoy.