Sweet Potato Gnocchi

INGREDIENTS

• 2 1-pound red-skinned sweet potatoes (yams), rinsed, patted dry, pierced all over with fork
• 1 12-ounce container fresh ricotta cheese, drained in sieve 2 hours
• 1 cup finely grated Parmesan cheese (about 3 ounces)
• 2 tablespoons (packed) golden brown sugar
• 2 teaspoons plus 2 tablespoons salt
• 1/2 teaspoon freshly ground nutmeg
• 2 3/4 cups (about) all purpose flour
• 1 cup (2 sticks) unsalted butter
• 6 tablespoons chopped fresh sage plus whole leaves for garnish