2 pounds new potatoes, peeled
About 11 tablespoons butter
Fine sea salt and freshly ground black pepper
2 onions, thinly sliced
A bunch of fresh parsley, leaves removed and finely chopped
Put the potatoes in a large pot, add enough salted cold water to cover, bring to a boil, and cook until parboiled, 10 to 15 minutes. Drain in a colander and rinse under cool running water. Let cool for a few minutes, then slice the potatoes into 1/8-inch thick slices.
In a large saute pan, melt 2 tablespoons of the butter. Add about one-quarter of the potatoes and fry, seasoning them with salt and pepper, until golden, about 6 minutes. Transfer to a plate. Continue frying the potatoes, adding more butter each time (you should use about 8 tablespoons in total), until all of them are cooked.
Meanwhile, in another saute pan, heat the remaining 2 tablespoons butter over medium heat. Cook the onions until golden, about 5 minutes.
Return all of the potatoes to the pan, add the onions, and mix gently. Cook for 5 more minutes for the flavors to combine.
Transfer the potatoes and onions to a large baking dish. Bake until gently sizzling, about 10 minutes.
Sprinkle the parsley over the potatoes and serve. Serves 4 to 6.