Use canned whole plum tomatoes in puree. Parmesan can be substituted for pecorino and Fontina can be substituted for Bel Paese cheese. Melt 1 Tbsp. butter with oil in heavy large saucepan over medium-low heat. Add onion, cover and cook until translucent, stirring occasionally, about 10 minutes. Add garlic and stir 1 minute. Blend in tomatoes. Increase heat to medium high and simmer uncovered until thickened, stirring occasionally, about 10 minutes. Season lightly with salt and generously with fresh ground pepper. Bring cream to boil in heavy large skillet. Reduce heat and simmer until slightly thickened, about 5 minutes. Stir in tomato sauce. Keep sauce warm. Cook pasta in large amount of boiling salted water until al dente. When pasta is almost done, return sauce to simmer. Add chicken to sauce and stir until pieces are just firm, about 2 minutes. Blend in cheeses and remaining 4 Tbsp. butter. Drain pasta. Add to sauce, tossing to coat. Adjust seasoning. Spoon mixture into heated bowls. Garnish with minced parsley and serve. Pass additional grated cheese separately.