Root Vegetable

This traditional Irish potato dish can be assembled up to 2 hours ahead and then browned just before serving.

To keep mashed potatoes warm for up to 2 hours, place them in a heatproof bowl over a pot filled with 3 inches of barely simmering water; cover to seal in the steam.

Halving the yams before roasting greatly reduces the cooking time and allows them to develop a nice golden crust.

A copper gratin dish or cast-iron skillet is ideal for roasting potatoes, but a rimmed baking sheet works equally well. To ensure the potatoes cook evenly, slice larger ones in half lengthwise and leave smaller ones whole.

Make sure to use at least a 5-quart saucepan so the oil won’t bubble over.

Because the potatoes are cooked and served whole, be sure to select those that are similar in size to ensure they cook evenly.

A Japanese or French mandoline is great for slicing vegetables uniformly—anywhere from very thin to thick—and takes much less time than slicing by hand with a knife.

For a less formal but equally appealing presentation, you can spoon rather than pipe the filling into the shells.

Using a mandoline to slice the potatoes is quick and easy. You can do so up to four hours ahead; to prevent browning, place matchsticks in a bowl of cold water in the refrigerator until ready to use, then pat them dry with paper towels.

This recipe can be made a day ahead and refrigerated; reheat before serving.