Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper and sprinkle with the coarse salt. Set aside.
Scrub the potatoes thoroughly and prick them with a fork. Place on the prepared baking sheet.
Bake for 50 to 60 minutes, or until the potatoes are tender and easily pierced with a fork. Let the potatoes cool slightly.
When the potatoes are cool enough to handle, peel them and pass them through a potato ricer or food mill into a large bowl.
Add the egg, egg yolk, kosher salt, and nutmeg to the potatoes.
In a separate bowl, whisk together the rice flour, tapioca flour, and xanthan gum.
Gradually add the flour mixture to the potatoes, stirring until a dough forms.
If the dough is too sticky, add a little more flour, 1 tbsp at a time.
Divide the dough into 4 equal pieces.
On a lightly floured surface, roll each piece of dough into a log about 1-inch thick.
Using a sharp knife, cut the logs into 1-inch pieces.
Roll each gnocchi piece over the tines of a fork to create a classic ridged shape or shape as desired.
Bring a large pot of salted water to a boil over high heat. Carefully drop the gnocchi into the boiling water. Cook for 2 to 3 minutes, or until they rise to the surface and are cooked through.
Drain the gnocchi and toss them with your favorite sauce. Serve immediately.