Put onion and garlic in food processor. Finely chop (or you can chop by hand). Coat large nonstick skillet and set over medium high heat. When skillet is hot, add olive oil, then onion and garlic and cook til onion and garlic begin to soften, 2 to 3 minutes. (I usually add the onion first and brown it a bit, then the garlic. If you add the garlic too soon, it will brown and burn and have a bitter taste). Meanwhile put carrots and celery in food process and finely chop. Add to skillet and cook 3 to 4 minutes more. Increase heat to high, add ground meats and break into small chunks with wooden spoon. Add salt and pepper. Cook til meat begins o brown, 3 to 4 minutes. Add tomatoes, broth and sugar. Reduce heat to low, cover and simmer, stirring occasionally for 30 minutes. Stir in sweet potato puree and Parmesan. Cook the pasta in large pot of salted boiling water as the package directs. Cook till al dente. Drain in strainer, then return to pot. Pour warm sauce over pasta and toss if you wish. Makes 4 servings.