Step 1

For the Gnocchi: Adjust oven rack to middle position, and preheat oven to 450°F (232°C). Set potatoes either on a wire rack set over a baking sheet, on a baking sheet lined with a layer of salt, or directly on the oven's racks. Bake until completely tender throughout when pierced with a fork, about 45 minutes. Transfer potatoes to a work surface; if making the dish start-to-finish, leave oven on. Using tongs to hold hot potatoes, slice each in half lengthwise.

Step 2

Using a spoon, scoop potato flesh into a ricer or food mill fitted with the finest disk. Press potato flesh onto a clean work surface, spreading it into an even layer, and allow steam to escape for a few minutes.

Step 3

Drizzle egg yolks all over. Sprinkle with 1 1/2 teaspoons salt.

Step 4

Scoop 3/4 cup (100g) flour into a fine-mesh strainer and tap to dust flour all over potatoes.

Step 5

Using pastry blender or bench scraper, chop down repeatedly all over to cut flour and egg into potato.

Step 6

Using a bench scraper, gather up shaggy potato mass and pat into a loose ball. Press ball flat with hands, then fold in half using bench scraper and press down again.

Step 7

Scoop remaining 1/4 cup (30g) flour into sieve and dust all over potato dough. Continue to gently fold and press, just until a uniform dough comes together; make sure to simply fold and press down and avoid the smearing motion more commonly used when kneading bread. Add additional flour as necessary to achieve a dough that's tender and moist yet can hold its shape, but not wet and sticky (whether you need more flour, and how much you might need, will depend on natural moisture content of the potatoes you use, which is highly variable, but a dough that's too wet and pasty is prone to falling apart when boiled and baked later).

Step 8

Dust potato dough all over with flour and gently form into a log.

Step 9

Clean work area well and dust with fresh flour. Using bench scraper, slice off a roughly 2-inch-thick portion of dough and roll into a snake about 1/2 inch thick; use a light touch as you roll, trying to use your palms more than your fingers, and dusting as necessary with flour to prevent sticking.

Step 10

Using bench scraper, cut snake into 1-inch portions, trimming off uneven ends as necessary. If desired, gently roll each gnocco on the tines of a fork to give it a ridged exterior. Transfer gnocchi to a well-floured area or baking sheet and repeat with remaining dough. If not cooking recipe start-to-finish, baking sheet of gnocchi can be transferred to the freezer at this point (see make-ahead and storage section for full freezing instructions).

Step 11

For the Sauce and to Serve: Bring a large pot of salted water to a simmer over medium-high heat. Meanwhile, in a 3-quart saucier or 12-inch stainless-steel skillet, combine cream, Fontina, butter, a pinch of black pepper, and nutmeg.

Step 12

Set over medium heat and cook, whisking constantly, until butter and cheese are fully melted and a smooth, silky sauce has formed, about 4 minutes. Season with salt, but only if necessary. Keep warm, stirring frequently to prevent a skin from forming.

Step 13

Working in batches to prevent crowding the pot, add gnocchi to simmering water and cook, gently shaking the pot as needed to keep them from sticking, until they float to the surface. Using a spider skimmer, lift floating gnocchi from the water and let drain, then transfer to cheese sauce. Toss very gently with a large spoon to coat, being careful not to break gnocchi. Repeat with remaining gnocchi and toss gently once more to coat.

Step 14

Remove from heat. Divide gnocchi and sauce between warmed serving bowls, top each portion with grated nutmeg, and serve.