Cut the potatoes into cubes and cook in boiling water for 10 minutes.
Spread butter and olive oil on the bottom of the iron plate, place the potatoes on top, sprinkle with black pepper and salt, and bake in the oven for 190 degrees for 17 to 20 minutes.
Remove the iron plate, press the potatoes slightly flat (I use a large spoon), sprinkle with vinegar, olive oil, rosemary, put the garlic in the oven and bake for 15 to 20 minutes.
To the outer skin becomes golden yellow