Venice and gnocchi — Les Petites Gourmettes

Ingredients

• 2 pounds sweet potatoes
• 1 heaping cup ricotta cheese, drained in a sieve placed over a bowl for 1 hour
• 3/4 cup grated Parmesan cheese
• 2 tablespoons golden brown sugar
• 1 1/2 teaspoons salt (for boiling water)
• 1/2 teaspoon freshly ground nutmeg
• 1 1/2 cups (about) flour
• 2 tablespoons unsalted butter
• 1/4 cup chopped fresh sage plus whole leaves for garnish