To die for: For purple sweet potato gnocchi dough


3/4 pound purple-fleshed sweet potato
1/4 cup all-purpose unbleached flour, plus additional for the work surface
Zest of one navel orange
1/2 teaspoon freshly grated nutmeg
1/2 teaspoon fine sea salt
For orange sweet potato dough
1/2 pound orange-fleshed sweet potato, such as Covingtons
1/2 cup all-purpose unbleached flour, plus additional for the work surface
Zest of one navel orange
1/2 teaspoon freshly grated nutmeg
1/2 teaspoon fine sea salt
For cooking
kosher salt
For serving
3 tablespoons unsalted butter, melted
1/4 cup lightly toasted hazelnuts, skins rubbed off, chopped finely

2 tablespoons freshly grated Parmigiano-Reggiano cheese