Step 1: Roast the sweet potatoes at 400°F (200°C) for about 45-60 minutes until tender. Allow them to cool, then peel and mash the flesh until completely smooth using a potato ricer or masher.
Step 2: In a large mixing bowl, combine the mashed sweet potato, drained ricotta, beaten egg, salt, and nutmeg. Stir until well combined.
Step 3: Gradually add the flour, half a cup at a time, mixing gently until a soft dough forms. Move to a floured surface and knead very lightly for about 1 minute. The dough should be soft and slightly tacky, but not stick to your hands.
Step 4: Divide the dough into 4 sections. Roll each section into a long rope about 1/2 inch thick. Cut the ropes into 1-inch pieces. Optionally, roll them over a fork to create ridges.
Step 5: Bring a large pot of salted water to a boil. Drop the gnocchi in batches. Once they float to the surface (about 2-3 minutes), let them cook for another 30 seconds, then remove with a slotted spoon.
Step 6: In a large skillet over medium heat, melt the butter. Cook until it begins to foam and turn a light brown color with a nutty aroma. Add the fresh sage leaves and fry until they are crisp.
Step 7: Add the boiled gnocchi directly to the skillet with the brown butter. Pan-sear for 1-2 minutes until the gnocchi have golden edges. Toss gently to coat with the sauce.
Step 8: Serve immediately topped with grated Parmesan cheese and a crack of fresh black pepper.