In a large skillet, over medium heat, warm the olive oil.
Add the onion and saute until golden, 6 - 8 minutes.
Add the garlic, and cook for another minute.
Stir in the sausage, beef, and a healthy pinch of salt and pepper.
Cook, stirring and breaking up the meat with a wooden spoon, until meat is browned, about 7-8 minutes. At this point, if too much fat has rendered, tilt the skillet and remove excess with spoon (leave some, or all...it will incorporate as it cooks down).
Add the tomatoes and puree, and simmer until the sauce has thickened, about 15 - 20 minutes.
Stir in basil and set aside.