If you don't have crushed tomatoes on hand, there are a couple options. You can use plain tomato sauce (24 ounces) + tomato paste (4 ounces) OR you could use a 28 ounce can of diced tomatoes and put them through the food processor to cut them into smaller pieces (crushed vs diced). In a real pinch, you could use some spaghetti sauce or tomato soup in place of the crushed tomatoes.