Gnocchi Gratin

Bake the potatoes
Position a rack in the middle of an oven and preheat to 350°F. Using the tines of a fork, prick the potatoes once or twice about 1/4 inch deep. This allows them to release steam as they bake so the potato flesh is fairly dry when they finish cooking. Place the potatoes directly on the oven rack and bake until the flesh is very tender when pierced with a small knife, about 1 1/2 hours. Using pot holders, remove the potatoes from the oven and set them on the counter to cool.

"Rice" the potatoes
When the potatoes are just cool enough to handle, cut them in half lengthwise. Using a large metal spoon, scoop out the potato flesh from the skins. Fit a ricer or a food mill with the disk with the small holes. Force the potato flesh through the ricer or mill, allowing it to fall onto a large rimmed baking sheet. Using a heatproof silicone spatula, spread out the potato flesh on the sheet and let it cool completely. This step allows excess moisture to evaporate so that the potatoes are as dry as possible when you make the dough.

Make the gnocchi dough
Break the eggs into a bowl and check for shell bits. Add the salt and beat the eggs with a fork until blended. When the potatoes are completely cool, drizzle them evenly with the egg mixture. Then sprinkle 1 cup of the flour evenly over the potatoes. Using a bench scraper, scoop, lift and fold the potatoes to mix them with the eggs and flour until a coarse dough forms. It should look raggedy. Mixing the dough this way, by hand, helps keep the texture of the gnocchi light and delicate.

Adjust the dough consistency and divide the dough
Sprinkle 1/4 cup of the remaining flour on a wood or slightly rough plastic work surface. Spread the potato mixture on the surface and sprinkle with another 1/4 cup of flour. Using the bench scraper and then your hands, scoop, lift and fold the mixture, lightly pressing it as you work, until the flour is incorporated. Work in only as much of the final 1/2 cup flour as needed for a smooth dough. Shape the dough into a ball, dust with flour and cover with an overturned bowl. Dust 2 large rimmed baking sheets with flour. Using the bench scraper, scrape the work surface clean and then dust it with flour. Cut the dough into 8 equal pieces. Slip 7 of the pieces back under the bowl.

Roll the dough into a log
Place 1 dough piece in the center of the surface and shape it into a short cylinder. Using the fingers of both hands, roll the dough back and forth over the surface, gradually shifting your hands to the ends, to elongate it slowly into a narrow log about 1/2 inch in diameter.

Cut the log into pieces
Use a bench scraper or knife to cut the log into 3/4-inch pillow-shaped pieces. Place the pieces in a single layer, not touching, on the baking sheets. Roll and cut the remaining dough pieces in the same way. Cover the baking sheets with aluminum foil and refrigerate for at least 1 hour or up to overnight.

Make the white sauce
In a small saucepan over medium heat, warm the milk. Place a nonreactive saucepan over medium-low heat and add the butter. When the butter has melted, add the flour and cook, stirring constantly, until the mixture forms a roux, 2 to 3 minutes. Remove from the heat and slowly add the hot milk while whisking constantly. Add the salt, return to medium heat and cook, stirring constantly, until the sauce is smooth and thick enough to coat the back of a spoon, about 1 minute. Remove from the heat.

Ready your ingredients and equipment
Finely grate the cheese using the small grating holes of a box grater-shredder or a rasp grater. Set the cheese aside. Position a rack in the middle of the oven and preheat to 400°F. Butter a 9-by-13-by-2-inch baking dish. Bring a large pot three-fourths full of water to a rolling boil and add about 2 Tbs. salt. Have ready a colander set over a bowl or in the sink.

Cook the gnocchi
A few at a time, drop half of the gnocchi into the boiling water and stir them gently to prevent sticking. Let the gnocchi cook until they rise to the surface. This should take only about 3 minutes. To test the gnocchi for doneness, use a slotted spoon to remove one and use a paring knife to cut it in half. Bite into it; it should be tender throughout with no raw flour flavor. Using the slotted spoon, scoop out the gnocchi and place them in the colander to drain for a few seconds. Return the water to a rolling boil, add the remaining gnocchi, and cook and drain them as you did the first half.

Assemble the gratin
While the second batch of gnocchi is cooking, transfer the first batch to the prepared baking dish. Top the gnocchi with half of the white sauce and then half the cheese. Top with the second batch of drained gnocchi, pour on the remaining sauce and sprinkle with the remaining cheese. Cut the butter into small bits and dot them over the sauce. Sprinkle evenly with the bread crumbs.

Bake and serve the gratin
Bake the gratin until the sauce is bubbling around the edges, the top is golden brown and a knife inserted in the center comes out hot to the touch, about 30 minutes. Remove the dish from the oven, place on a wire rack and let rest for about 10 minutes. Scoop out portions of the gnocchi with a large metal spoon, making sure each serving gets some of the golden brown top. Serves 6 to 8.

Chefs Tip: Don't try to make these dumplings with another potato variety. They will not have the proper starch and moisture content and thus will lack the correct texture.

Make-Ahead Tip: This dish can be assembled and then refrigerated, covered tightly, for up to 24 hours before baking. You may need to add as much as 15 minutes to the cooking time. After it has baked for about 30 minutes, start checking it every 5 minutes to see if it is ready.

Adapted from Williams-Sonoma Mastering Series, Pasta, Noodles & Dumplings, by Michele Scicolone (Simon & Schuster, 2005).