Heat oven to 350°F.
Melt 3 tablespoons butter in sauté pan. Add onion and cook over low until soft and caramelized. Set aside.
Cook sausage in skillet, breaking it apart with spoon into crumbles. Remove from heat and drain.
Cook pasta according to package directions, heavily salting the water. Drain and rinse briefly with cool water. Set aside.
Melt remaining 6 tablespoons butter. Sprinkle in flour, whisking to form soft roux. Cook until golden brown and bubbly, stirring; slowly pour in milk. Bring almost to boiling point, stirring constantly until sauce thickens. Add garlic, pepper and brie, mixing until smooth. Fold in prepared pasta, sausage, caramelized onion and dried apricots.
Pour mac and cheese mixture into 9x13-inch casserole dish; top with breadcrumbs. Bake 20 minutes or until golden brown. Serve immediately.