Preheat oven to 400 degrees. In a 5-quart pot, cook sausage over medium heat, stirring often, until browned, about 5 minutes. Stir in onions; cover, and cook until softened, 5 minutes. Uncover; cook, stirring occasionally, until golden brown, 10 to 15 minutes. Add garlic; cook 2 minutes. Transfer to a large bowl.