Preheat the oven to 375º.   

Place the sweet potatoes on a parchment-lined sheet tray, and roast until they are knife tender, about 45 minutes. Allow to cool.

While the sweet potatoes are roasting, bring a large pot of salted water to a boil. Keep at a low boil until ready to use.   

Peel the skin off the roasted potatoes and discard. Place the potatoes in a medium-size bowl, and using a potato masher, mash until smooth.   

Add the eggs, salt, cinnamon and nutmeg. Add enough flour to form a soft dough.

Turn the dough out onto a lightly-floured surface, and divide into 4 pieces. Roll each piece into a rope about 1/2 inch thick. Cut the ropes into 1-inch pieces, and place on a lightly-floured sheet tray. Set aside.

To make the sauce, heat a large sauté pan over medium-low heat and add the butter. Cook the butter until the milk solids begin to turn golden brown. Reduce the heat to low.

Drop the gnocchi in the boiling water, and cook until they float to the top. Continue to cook for an additional 1 to 2 minutes, or until they are cooked all the way through.

While the gnocchi is cooking, finish the sauce. Place the sage leaves in the browned butter, allowing them to cook for about 30 seconds.

Remove the sauce from the heat, and finish the sauce with lemon juice, and season with salt and pepper to taste.

Using a skimmer, transfer the gnocchi to the pan with the sauce and toss well.

Transfer to a platter, and top with Parmesan cheese.