Crumble ground beef and sausage into large saute pan. Cook over medium heat, stirring often, until no pink remains. Add onions and garlic and continue to cook until onions become soft and meat begins to brown. Form a "well" in the center of the pan by moving the meats and onions to the edge. Drop the tomato paste into the well and cook for an additional 2-3 minutes.
Stir 3 tomato paste cans full of water into the pan; stir. Add the canned tomatoes and pepper flakes. Lower the heat to simmer; cover and cook for at least 2 hours, stirring occasionally and adding more water as necessary if the mixture appears to be dry. (You don't want it to stick to the bottom of the pan and burn).