Scrub potato and poke several times with a fork. Set directly on the rack of a 400-degree oven and bake until tender when poked, about 45 minutes, or zap until tender, about 10 minutes.
When cool enough to handle, press through a potato ricer onto a work surface. Let cool until no longer steaming.
Whisk together egg, nutmeg and 1/8 teaspoon salt. Pour egg mixture over riced potato and stir very gently with a fork, just to combine. Sprinkle on about 1/3 cup flour and continue to mix very gently and sparingly with fork or fingers until a soft dough forms.
Heat a large pot of salted water to a boil. Pinch off a bit of dough and drop it in. If it holds its shape, you're good to go. If it falls apart, add a little more flour to the dough.
Divide dough in two. On a floured surface, roll each portion into a ½-inch thick rope. Slice crosswise into ½-inch segments.
Flip a fork over. Roll each gnocchi down the back of the fork, pressing lightly, to imprint grooves. Not absolutely necessary, but what's the point of gnocchi if not looking adorable?
Drop gnocchi into boiling water in 2 batches. Gnocchi will sink. Then, in about 1 minute, float. Wait 10 seconds. Scoop out gnocchi with a slotted spoon and drain on a clean kitchen towel.
Heat butter over medium-high heat in a medium skillet. It will melt, then brown. Add sage, sizzle 1 minute. Add cooked gnocchi and toast, tossing gently until lightly browned, about 1 minute. Enjoy as an appetizer or scatter on an arugula salad as surprising croutons.
Leah Eskin is a Tribune Newspapers special contributor. Email her at firstname.lastname@example.org.