Gnocchi Gratin with Gorgonzola Dolce

Name: Gnocchi Gratin with Gorgonzola Dolce
Ingredients: 1 pound russet potatoes; 1 large egg; 1 large egg yolk; 6 ounces Parmesan, finely grated, divided; 1 cup all-purpose flour plus more; 1 teaspoon kosher salt plus more; 1/2 teaspoon freshly grated nutmeg; 1 cup heavy cream; 1 sprig rosemary; 1 1/4-thick slice fresh ginger; 2 tablespoons (1/4 stick) unsalted butter, room temperature, divided; 3 tablespoons fine dried breadcrumbs; 4 ounces Gorgonzola dolce or other mild blue cheese; A 1 1/2-quart baking dish or gratin dish; a ricer