Heat olive oil in a large pot over medium heat.
Add the Italian sausage, breaking it up with a spoon, and cook until browned and cooked through, about 5-7 minutes.
Add the chopped onion and cook until softened, about 3 minutes.
Stir in the minced garlic and cook for 1 minute until fragrant.
Pour in the chicken broth and whole milk, then add the uncooked penne pasta, dried oregano, dried basil, crushed red pepper flakes, salt, and black pepper.
Bring the mixture to a boil, then reduce heat to medium-low and simmer, stirring occasionally, until the pasta is tender and most of the liquid is absorbed, about 12-15 minutes.
Remove the pot from heat and stir in the grated Parmesan cheese until melted and creamy.
Sprinkle chopped fresh parsley over the top before serving.