Wash and peel the potatoes and chop into thin round slices.
Grease the casserole dish with butter and layer the sliced potatoes across.
Add any optional ingredients (smoked ham, etc) in between the potato slices.
Cook in preheated oven for 25 minutes at 200C° (400F°) until potatoes and cheese are lightly browned.
While waiting, mix garlic, parmesan, paprika, salt and pepper in a bowl, along with any remaining melted butter.
Once the 35 minutes of cooking is done, add the parmesan mixture over the top of the potatoes in the casserole.
Add a few leaves of parsley on top for decoration.
Continue cooking in oven for 25 minutes at 400F° ( 200C°) until potatoes and cheese are lightly browned.
Serve while warm.
Notes
If in a hurry, you can lightly boil the potatoes the night before to cut down the cooking time in the oven. Put in the Instant pot for 8 minutes high pressure with quick release, peel them and then put them overnight in the fridge. The next day, slice the potatoes, add the sauce and put in preheated oven for 20 minutes. (Precook the bacon if you are adding it to the recipe.)