Lightly scrub the sweet potatoes under cold running water. Prick the sweet potato several times with a fork. Place the potatoes on a roasting tray and bake until tender, about 45 minutes. Remove from oven and cool..
Cook noodles in a large pot of boiling water until just tender, 7 to 9 minutes. Drain; set aside.
Heat the oil in a large pot on medium-high heat. Add the onions and cook for 5 minutes.
Add the garlic and cook for a minute more.
Add the flour and cook, stirring for 2 minutes.
Whisk in the chicken broth and the milk and simmer, stirring for 5 minutes.
Stir in the cheeses, the dijon mustard, nutmeg and salt.
Simmer for about 5 minutes until cheese is melted.
Stir in the cooked noodles, mashed sweet potatoes and bacon.
Transfer to a buttered baking dish.
Make the topping by combining the bread crumbs, melted butter and parmesan cheese.
Spoon the topping over the macaroni and cheese.
Bake for 20 minutes or until topping is golden brown in a 375 degree oven.