Unsalted butter, softened (for the pan)
2 lb. boiling potatoes, such as round whites from Maine or Long Island
1 heaping tbsp. coarse sea salt
4 tbsp. unsalted butter, softened
1 med. onion, finely chopped
Sea salt and freshly ground black pepper to taste
Freshly grated nutmeg to taste
4 lg. egg yolks
4 oz. unsmoked salt-cured ham, such as prosciutto, coarsely chopped
1/4 c. fresh chives, snipped with a scissors

1. Preheat the oven to 300 degrees. Coat the bottom and sides of the cake pan with butter. Set aside.

2. Peel and rinse the potatoes. Place in a saucepan, and cover generously with cold water. Add the salt and cook over moderate heat -- do not boil -- until a skewer inserted in a potato comes away easily, about 20 minutes.

3. Meanwhile, in a medium skillet, combine 1 tablespoon of the butter and the onions over moderate heat. Season lightly, and cook until the onions are soft and translucent, 3 to 4 minutes. Set aside.

4. As soon as the potatoes are cooked, drain them well. Pass them through the fine grid of a food mill into a large mixing bowl. (If the potatoes are large, you may want to halve or quarter them before passing through the mill.) With a wooden spoon, stir in the nutmeg, the remaining 3 tablespoons butter, and the egg yolks, one at a time. Continue stirring vigorously until the butter and egg yolks are thoroughly incorporated. The mixture will be thick and slippery.

5. Fold the onions, ham, and chives into the potato mixture. Transfer the mixture to the cake pan, and smooth it out with the back of a spoon. Place it in the center of the oven and bake, uncovered, until the potato cake is firm and the top is browned, 45 to 50 minutes.

6. Remove the potato cake from the oven and transfer it, browned-side up (for the golden top side is the prettier), to a large platter. Slice into wedges and serve warm or at room temperature.

Yield: 6 to 8 servings.

VARIATION: For very pretty individual potato cakes, bake these in nonstick muffin tins. Alternatively, bake the cake in a single 10 1/2-inch round porcelain baking dish.