Bring a large pot of lightly salted water to a boil. Add penne and cook, stirring occasionally, until tender yet firm to the bite, about 11 minutes. Drain, reserving 1 cup of cooking water.
Heat olive oil in a large skillet over medium heat and cook onion until soft and translucent while penne is cooking, about 5 minutes. Add garlic and cook an additional 30 seconds. Stir in tomato sauce and tomato paste and cook until slightly reduced, about 5 minutes. Add cream and Parmesan cheese and season with salt, pepper, and sugar.
Preheat oven to 400 degrees F (200 degrees C). Grease a baking dish.
Stir some pasta cooking water into the sauce and add cooked penne. Remove from heat and stir in cherry tomatoes, 1/2 the mozzarella cheese, and basil. Pour penne mixture into the prepared baking dish and cover with remaining mozzarella cheese.
Bake in the preheated oven until cheese is melted, about 20 minutes