Bring a large pot of salted water to a boil and cook the rotini until al dente according to package directions; reserve about 1/2 cup of the pasta cooking water, then drain the pasta.
While the pasta cooks, heat the butter and olive oil in a large skillet over medium heat until the butter melts.
Add the chopped onion and cook 3 to 5 minutes until softened and translucent.
Add the minced garlic and cook about 30 seconds until fragrant.
Stir in the tomato passata, Italian seasoning, crumbled bouillon cube, sugar, red pepper flakes, salt, and black pepper; bring to a simmer and cook about 5 minutes.
Pour in the half and half, stir, and simmer 2 to 3 minutes until the sauce is slightly thickened.
Add the cooked pasta and shredded mozzarella to the skillet and toss to combine, cooking a few minutes until the pasta is warmed through and the cheese melts; add reserved pasta water a splash at a time if the sauce is too thick.
Garnish with parsley or basil and freshly grated Parmesan if desired, then serve immediately.